Drawstring pants?

Finally finished up my pants for Ridiculously Skinny 3 year old, and I messed up the elastic and basically, it isn't doing anything to keep his pants up right now. Since I have to go back in and adjust, I asked him, and he said he'd prefer a drawstring. Thoughts on feasibility? I feel like this should be a simple "make long drawstring (maybe with elastic in the middle), run through elastic casing (not forgetting to make holes for the ends)", but I'd appreciate some more experienced reassurance. Thanks!