Filling holes in transom

[McGillicuddy]

Greetings Pilgrims,
Kind of a basic question and probably been awswered a million times but here it is:
I removed a bunch of stuff from the transoms and wonder how to best seal the holes. Holes range from #6 x 1/2" screws from clamshells, to 1/4" holes all the way through from dive ladder. Oh, yeah, also 1/2" holes from trim tab hoses, and a bunch of #12 x 1-1/4 from the tab mounting plates.

Obviously I'll be fighting gravity while filling the holes ,so I was thinking I could make little half cups from modeling clay and attach them to each side of the transom to eliminate running and sagging, thereby keeping the holes flooded with some neat or slightly thickened epoxy until it sets. Any thoughts on this method?

Anybody know a better way? Thanks. Happy Thanksgiving, Pilgrims.