heres a couple of off the wall ways to approach filling the holes. #1 ever seen those little umbrellas that they put in exotic drinks like mai tais? get some of those. maybe trim them so the diameter of the open umbrella is 1" or so. insert into the hole, back it up till it opens, then pack around the stem with epoxy paste (marine tex is good) until you think you have a little mushroom of epoxy backed up against the inside wall of the transom.( i would try this on a piece of thin plywood or illustration board for practice.) let it set, then drill (tap) for screws. #2 okay heres a real off the wall solution. get a six pack of beer, two friends, epoxy paste as above, a glue syringe (hardware stores with west system epoxy have them) and some masking tape. stand the boat upright with the bow in the air against a tree, building, or whatever, get the boat vertical bows up. have your friends lift the boat while you use the syringe to squirt the epoxy paste up into the holes. use enough so that it puddles some inside the boat. tape off the holes so the glue doesnt run out . set the boat down (still as vertical as possible) tie or prop the boat so it wont fall and come back when the glue left over in the mixing pot firms up. remember that epoxy needs clean dry surfaces to adhere. tap for screws after it sets up hard 24 hours. wacky or what!