Strategies for a Startup within a Big Company

I have an idea for a product that is close enough in concept to my employer's business that they might have a claim on the IP (not a valid claim, IMO, but they have all the lawyers). It's unlikely that I could persuade my employer to build the product as it wouldn't fit in with their brand.

I'd like to approach my employer about creative ideas - such as a separate legal entity within the company, possibly with additional outside funding - for building the product within the company. This question asks about creating a separate "startup". What other strategies I should consider?

Many large companies format their innovation pipeline to allow things like this, but if the company doesn't already do it, I wouldn't hold your breath.

Would this product be in competition with your employers brand? Do you use proprietary technology that your employer owns? Was this product developed on company time?

If the answer to any of those questions is "yes" then you can't make this company on your own, you would either need a release from the company, or they would have to be the ones heading it up. If the answer to all those questions is "no" you might be able to start your own company, and develop the technology yourself. It depends on the environment of the company, and what forms you have signed as part of your employment. Either which way, you need to gather any applicable documents, and take them to an IP lawyer to make sure you're in the clear before you do anything.