when I lived in kansas, i used to use my NX bottle warmer on my intake manifold, it did help alot with cold start, mazdaspeed proteges were notorious for having sh** cold start maps. my hypothesis was, hot air will make fuel evaporate off the head walls and ignite easier.
i had it hooked up to a battery charger for 12v supply, would lay it on the manifold and go inside
morning came around, i would plug in the extension cord i had running from it to my house inside before i hopped in the shower.
start up fine every time
also, if you want to heat the fuel, i remember my dad on his old chevelle would run coiled up hard fuel line inside a coffee can mounted in the engine bay with ice in it to cool the fuel (more fuel per volume) so i imagine something like this would work if you coiled it around a heat source.
some of the airplanes run the fuel line near the exhaust to warm it as well.