How do I best warm up my hedgehog?

My father hates having the heat on( he finally agreed to turn it on tho), but since fall has been blowing in, it has increasingly been getting colder. My hedgehog has been sleeping a lot, his belly is chilly. I know that this is not good, because he's trying to go into some sort of hibernation. But he's always sleeping, very sluggish, and he won't eat. Right now he is on my tummy inside my jacket (with a gap so he can breathe of course), I'm trying to warm him. Are there any other methods I can try? Once I do get him warmed up, I'll be putting fleece in his sleeping box and a warm blanket around his living area to better keep him warm. But how can I best warm him up now?