How about using acetone to dissolve the epoxy?
Acetone is the usual solvent for super glues (cyanoacrylates). It is
not especially effective on epoxies. The commercial solvent,
"Attack", which if I remember right is mostly methylene chloride (is
that right? not sure I'm remembering that right) works better.
But test before using, and be very certain exactly what the stone
is, ie a good piece of amber, or one of the treated or otherwise not
quite natural versions.
Even the best saber is also a resin, and not resistant to all
solvents. Amber also can vary some from sample to sample, so some
pieces might be more affected by any given solvent than others.
And as I mentioned above, you have to be careful, as some of what is
sold as amber, isn't exactly so, but another resin, usually copal, or
an imitation, or a reconstituted amber, which may also behave
differently from amber itself. Some of them look very convincingly
real. One also occasionally encounters pieces that are in effect,
lots of bits of amber in an epoxy or other resin matrix. These fakes,
if done with epoxy, obviously would be affected by any solvent that
also attacks epoxy glues