How about a disposable hand warmers.

 

There were a lot of people using those outside, but when you shoot them, they spill out and the are only good for a couple of shots.

I think I will have to try the aluminum tape and hope it works.

 

Okay came up with another idea. Ir flashlight on a tripod aimed at the target .

 

Let us know if the IR light works. Foil tape indoors didn’t work for me, at 100 yards it was a very faint image.