User created content in shop theme

I have been struggling with figuring out how to allow users to upload products and I came across some forum topics stating that the comparison theme allows you to do that. Is there a way to port that functionality into the responsive shop theme?
I looked at the demo theme for the comparison, and it is exactly what I need. I want to be able to restrict some fields later. Like only allow them to add downloadable products with a price of $0, etc…
Any thoughts on how to do that?
Thanks,
Hassane