That's what I did years back to use them for mold walls in resin casting. They don't leak and the latex peels right off when cured.
Now that I can't do resin casting any more (chemical contamination) and the kids are grown up and moved out I found another use for them. Jigs for assembling and painting models. Really useful for getting the right sit for undercarriages and angles for wings, especially parasol and biplanes. No more shaking fingers for that tiny rigging job.
Cheap, too. I saw a set of 400 pieces for $5.99 at Toys R' Us the other day.