[JamesBarney]

> When I asked my co-founder for rights to use the existing code in my new venture, he refused, citing concerns over sharing IP.

If this is a actually a good idea, then I'd try to find a new technical co-founder.

If you really think the IP is valuable (which I doubt considering you don't have any users), I'd focus on why your co-founder won't sell you the code for a % of the company. What are his concerns over sharing IP?