What if you put the shirt in the freezer long enough for the epoxy to freeze solid and get brittle enough to break off? I think maybe two to three hours would be enough. Hope that works.
Epoxy is considered a permanent adhesive. However, if you need to remove it, apply Easy-Off Oven Cleaner to the epoxy and let it sit for awhile. Eventually, the epoxy will soften and can be pried from the surface with a putty knife. Remember to test the oven cleaner on an inconspicuous area before applying over a large area.