shield startup from employment IP agreement

Since I travel between SG & KL, the short answer is it depends on the precise wording of the contract. In general courts consider anything done for the purpose of employment, eg hired to invent, using firm equipment or on company times, even use of customer lists (a potential commercial secret) to be owned by them. You can either get a waiver (eg volunteer open-source coding), buy them out (ie pay fair market price but have IP owned by you) or negotiate a compromise where in return for a slice of equity, you can tap into existing background IP (see group Spinout Meister). What courts tend to frown upon are onerous non-compete clauses, trying to limiting working knowledge (as compared with firm specific data) and anti-competitive behaviour. So it comes down to whether you see the existing employer as help or hindrance in the near future ... note the very fact that you are doing 2 jobs might make some companies nervous if they feel you are not giving 100% at work, especially if you are hinting you want to jump ship and taking colleagues with you.