For some reason, a leaf blower comes to mind.
Discussion
I’m thinking of hooking it up to perforated drainage tubing, so it moves the air down, but lets it out a little along the way.
this might sound stupid but something like a large rubber 'whoopie cushion' esque material that you could blow air in a hole, lay it down on the spot you want melted, and poke a hole in opposite side side so air can get out. as long as hot air flowing and the heat is transferred somewhat through the material...would work 🤷♂️
Leaning towards perforated tubing of some sorts, so kinda like that! Either PVC or corrugated, unsure which yet.