What about an
immersion heater? You could make a custom intake pipe with a hole to fit the heating element.
This one has a screw on it. You could make a hole with threads in the pipe so it screws in without having a vacuum leak.
Screw-in Immersion Heater
Don't know what you'll be able to do with the voltage issue. There is a 12V adapter version.
12V Immersion Heater
I have to agree with others. I think it would be more beneficial to do this to the coolant rather than the air intake, because the ECU runs rich until the coolant is up to temp. If you heat the air intake, it is like treating the symptom, heating the coolant is fixing the problem. Maybe you should try this with the coolant and if it works, but isn't enough, than you can pick the higher hanging fruit and heat the air intake.
I like the idea.
