shield startup from employment IP agreement

That's a tough one on several levels - first, I would check your current contract to see if there is anything in there that differentiates whether you create the IP on company time or on personal time - sometimes contracts are drafted that way whereby if you create something on your own personal time, the IP is yours, not the company because you did not create it while actually working for the company. If your contract is silent as to that issue, then you may have some difficulties - your current company can claim that your IP creations are company IP, or if you effectively ask to "rewrite" your contract so as to spell out the separation of company time and personal/private time, your company will obviously know what you are up to and could lead to unpleasant circumstances for you on your current job or you could be asked to leave. I would consult a good contract attorney.