I think your biggest issue would be gaining trust for new users. It is a fact most people will be doubthful atfirst. Other than that, it is hard to say wether it would work or not. Obviously it was never tried before.
Thanks you! Best answer here! Never tried so how would it be a ponzi! Thank you for the feedback!
NP. I have an idea. If you accept payments via paypal, you might attract more people as it might be an alternative, easy way of buy some extra bitcoin with couple dollars people have in their paypal account.