That is not an attractive option relative to e.g. being an affiliate of the company and getting 10% of the sales price (or much more) for no up-front investment and no sales work. They're not necessarily competitive options vis-a-vis a single company, but if you offered terms like that, I predict no savvy person taking you up on them.
A more viable approach to generating cash early in the life of a company is to pre-sell a particular product which is either time-bounded or feature-bounded in return for a largish sum of cash paid up-front. For example, Joyent used to be a fairly attractive option for Rails hosting, and they had a shared server offering where you could buy a lifetime membership on a particular tier for a few hundred dollars. Selling ~6 of those memberships buys you the physical machine to host many more than 6 of them, meaning they raised enough capital to buy machines (or demonstrate creditworthiness to Dell) to have available inventory for more traditional hosting plans.
Slicehost similarly had a massive cash flow crunch at one point which was preventing them from buying hardware to service new customers for their VPS offering, back when VPSes were quite new and Slicehost was heads-and-tails the best game around. They had an amusing auction-like mechanic: they sorted their waitlist by the dollar value you were willing to pre-pay, so if (for example) you wanted the $20 a month VPS but were willing to pre-pay for the first 6 months, you got in earlier than someone willing to prepay 3 months or desiring month-to-month. This essentially let Slicehost borrow e.g. Bingo Card Creator's credit cards to buy new servers from Dell, without ever needing to offer any sort of equity or do anything very tricky with accounting. (Book $1,000 of cash as assets and $1,000 of unearned revenue as liabilities, spend $1,000 cash from assets and add $1,000 of servers to assets, gradually debit unearned revenue as I consume services every month.)
Another example is Spreedly, which sold a particular plan for their SaaS service (I think they called them "Kickstarters", actually?) where you'd essentially pre-pay for 2 years of service and in return get service for life. It apparently worked out pretty well, though your accountant will hate you if you do that. A more typical example is a SaaS company offering you 10% off the monthly rate if you sign up for yearly billing and 15% off if you sign up for bi-yearly billing, which in both cases will tend to have the SaaS company get a whole bunch of cash upfront. (And the same accounting thing as Slicehost, above.)
A more viable approach to generating cash early in the life of a company is to pre-sell a particular product which is either time-bounded or feature-bounded in return for a largish sum of cash paid up-front. For example, Joyent used to be a fairly attractive option for Rails hosting, and they had a shared server offering where you could buy a lifetime membership on a particular tier for a few hundred dollars. Selling ~6 of those memberships buys you the physical machine to host many more than 6 of them, meaning they raised enough capital to buy machines (or demonstrate creditworthiness to Dell) to have available inventory for more traditional hosting plans.
Slicehost similarly had a massive cash flow crunch at one point which was preventing them from buying hardware to service new customers for their VPS offering, back when VPSes were quite new and Slicehost was heads-and-tails the best game around. They had an amusing auction-like mechanic: they sorted their waitlist by the dollar value you were willing to pre-pay, so if (for example) you wanted the $20 a month VPS but were willing to pre-pay for the first 6 months, you got in earlier than someone willing to prepay 3 months or desiring month-to-month. This essentially let Slicehost borrow e.g. Bingo Card Creator's credit cards to buy new servers from Dell, without ever needing to offer any sort of equity or do anything very tricky with accounting. (Book $1,000 of cash as assets and $1,000 of unearned revenue as liabilities, spend $1,000 cash from assets and add $1,000 of servers to assets, gradually debit unearned revenue as I consume services every month.)
Another example is Spreedly, which sold a particular plan for their SaaS service (I think they called them "Kickstarters", actually?) where you'd essentially pre-pay for 2 years of service and in return get service for life. It apparently worked out pretty well, though your accountant will hate you if you do that. A more typical example is a SaaS company offering you 10% off the monthly rate if you sign up for yearly billing and 15% off if you sign up for bi-yearly billing, which in both cases will tend to have the SaaS company get a whole bunch of cash upfront. (And the same accounting thing as Slicehost, above.)