How to attach hand IK to trolley handle bar

I'm a beginner working on a project where a shopper has to hold on to a trolley while walking around a supermarket.
Learning from the mechanim example scene....I got him to hold the handle bar at a key press. But I actually need him to be permanently holding on to the handle bars wit his left hand, while being able to change the right hand IK goal from the handle bar to another item with a key press. Any ideas on scripts content that could work (not really the script person but really wanna learn.