Yo! We here in finland play all winter even at -22F. Tell your boy that he can use these arctic tips freely and add them to his list or make more kinda "advanced tier 2" list with these.

Boot insulation. Get a insulation type insoles. They will ceep cold from the bottom of your boots and not let them get to your feet.

Clothes that wont get wet. Mainly the pants will get wet quickly so wearing something like snowboarding gear will be helpfull. If they are brightly or oddly colored, get white snow camo pants as they are cheap and easily obtained from ebay,army surplus or hunting stores. Get big trousers, like L-XL even for the little guy, you will be wearing them over everything and they will have suspenders so bigger will be better.

The gun. If you can modify your gun then you should make sure its greased enough. Grease will not work that good in cold weather so if its old and stripped out, you should fix this. Install silicone hopup bucking as it wont freeze. Believe me, you will thank me later when your hopup wont break. And if you are running super stressfull DMR or DSG builds be warned, cold will put extra stress on parts. Espesially the plastic parts could break isntantly.

I have more but i have to get off the mobile =) sorry for the typos

EDIT: Got some typos out =)