Hi Laramie, I hope all is well with you. Flying season is coming soon around here.
Your idea could work. But I have a spar (I think it's called a turbulator) right on the C/G in the wing. I put it there to hold the airfoil shape better. I'd have to cut that up. I think I'll wait till she gets ugly first. This one has stayed pretty longer than usual for my planes. The others are only pretty from a distance now.
Or I could get a skinny balloon if I could find a pack of them just the right size, and use it as a no-pressure bladder. Then I'd have to make a container for it so as not to soak the balsa.