: The question is, then: Has anyone tried using a caulking gun and a clean
: cartridge filled with thickened epoxy for making small fillets?

I have used this method, and it works quite well. The need for tooling the joint is not eliminated, however the overall job goes much quicker and neater. One caveat, with the garden variety caulk cartridge it is impossible to load the goop without putting in air bubbles too. The end caps just aren't vented. There are three solutions to this. One is to live with the occasional "burp" and splatter. Two is to stand the cartridge on end and try to vent the air out of the tip. Third is to find vented end caps (refer to my earlier post about twin-tube epoxy dispensers) that are inserted until epoxy oozes out the hole, and then cap it with the plug provided. These are much harder to find, but they work really slick.