Sounds like a perfect viral approach to me. So you find that once one of these called-in collaborators uses the product, they then instigate use on a separate i

Sounds like a perfect viral approach to me. So you find that once one of these called-in collaborators uses the product, they then instigate use on a separate independent project? That is, a viral/chain-reaction, not just one user inviting their immediate collaborators and it stops there? EDIT You're probably already on top of this, but (just thinking) if the collaborator-->instigator step is the problem, you could offer a discount for that specific conversion; the idea being not to make it more affordable, but to buy the bargain-seeking mindspace of "I wonder if there's a way I could grab this bargain?" (totally opposite of the article's "improve the app" approach).