Is firing a bow counted as 'use simple object'? because if it is (and lets face it, actually firing a bow (not drawing and aiming, which are probably counted as ready weapon) is pretty damned simple.
If it is, then the 0.25 point adept power Nimble Fingers allows you to use it as a free action.
If you can convince your GM that Initiating an ambush means you're not actually engaged in combat until your enemy reacts (good luck with that one) then multitasking adept power gives you another two free actions per initiative pass, allowing you to: Ready weapon (free), use simple object (free), Ready weapon (free), use simple object (simple action), Ready weapon for next turn (simple action)
because if you're going to break something, break it good and hard.