Not saying this idea is worth the complexity (sounds over-engineered), but I am pretty sure you could make like a 1"x2" can of compressed helium attached to a 3' balloon with a simple valve to pop open and inflate the balloon. Think of those little air cans that you use for refilling bike tires on the go. Only weigh a few grams, holds a lot of air.
Are you proposing that it could somehow hook itself up to a helium or hydrogen source, while hovering?