The technique I would use for bedding a 1/4" bolt would be drill the original hole with a 3/8" bit. Route
out the core
with a 3/8" diameter Dremel bit. The skinny shaft of the Dremel bit will let the cutting surface wallow out a pretty good radius. Then fill the hole with epoxy
. Now drill the 1/4" hole in the center and use a countersink to bevel the top edge so your sealant
will make a good bond.
Now you've got a thick plug
of epoxy firmly held in place by the top and bottom skins, and you've also got a margin all the way around the 1/4" fitting as well, just in case the second 1/4" hole is not perfectly centered over the 3/8" hole.