One of my best friends went through a very similar predicament with her startup a few years ago. She and her startup aren't technical, interestingly enough, but

One of my best friends went through a very similar predicament with her startup a few years ago. She and her startup aren't technical, interestingly enough, but she's been very successful, and has raised a fair amount of VC and angel money on the basis of very few a priori connections. She bootstrapped while on the job. I am not 100% sure how she managed that vis-a-vis her employer, but I'm guessing that she had a conversation with them and put her cards on the table, and that they came to an agreement of some sort. Incidentally, IANAL, but my understanding of those workplace IP agreements is that they only cover inventions and ideas you come up with "in the course of performing your job," or something to that effect. They do not cover nights and weekends. Read your contract's fine print, though, because there have been horror stories here. Hit me up over email (address in my profile) if you're interested in speaking to my friend about her experience. I'm also happy to help as best I can.