I fiddled around with hand warmers last year and landed on something similar for northeast bow hunting.
I am running a military / tactical chest rig - blue force gear rack minus with from right to left:
Fhf rangefinder pouch
Fhf Nino pouch
Molle gp admin pouch
I hooked the Fhf hand warmer to the bottom with a couple of molle grimlocks. It worked great. Never had an issue with it interfering with my bow shot or pack belt when I wore one.
Btw, like you, I could never get a kifaru in stock. I looked at a few other options including cabelas and UA. I bought one from another company and ran it for a few hunts but couldn't get my big hands inside it with a light tactical glove without a struggle. The Fhf is perfect fit wise for my hands with a thin glove.
Last thought, the hand warmer combo with a chemical warmer inside is a little piece of heaven in cold temps. I wore a bare right (draw) hand in 15 degree temps for multi hour stand sits. If you can think of a better way to keep hands warm and preserve dexterity, I am all in. For now, this works for me.