The weight is one thing. If you want to get out there badly enough and you don't have the coin for light gear or the time to make your own from scratch, you'll make do with heavy gear, as I do.

Staying warm is another thing altogether. Hypothermia is nothing to take chances with. I absolutely would not put him in a dangerous situation at any cost.

Maybe start with car camping and day-hikes, only fully-loaded to simulate backpacking and shakedown the gear. That way, you can keep extra warm stuff in the car close to hand or even bail if you need to.