Aaron, this it the approach I would take:
Get some this visqueen with tape to cover your entire wall face,
just in case.
Get a long enough one to cover your wall.
Buy, borrow, one of these:
or similar. The last one I bought was about $40. Make sure you
buy minimum expanding (little or no pressure/expansion) foam
You can add a length of clear plastic tubing to the tip to get
back in farther if you need to.
I'm glad you made me look - they have a foam that is already black
and doesn't require painting, even outdoors, that I didn't know
and a can of cleaner for the gun if you intend to keep it for
other work. If you don't clean the gun, throw it away - there is
no other way to salvage the gun. Buy several cans of foam,
especially if you can return what you don't use. Just looking I
would guess at 6 cans from what I see in the picture.
Once the foam is set up - next day- saw any excess foam off with a
serrated knife, Sawzall, hacksaw blade or similar. I would paint
it flat black to loose in the shadow line. Forget this one if
you use the black stuff.
They have a new fire version also:
Keep the whole world singing . . . .
Click to see the full signature.