Brainstorming ideas for coolant crossover on Air-Gap intakes

I'm running an Air-Gap intake on my Magnum-headed 360 and always had tuning issues with the fluctuations in temperature of this manifold. After adding a functional hood scoop with the air cleaner sealed off, even on a warm day the incoming cold air being sucked in causes my intake to cool down... Goes like this: Engine is cold, start it up, intake gets colder from vacuum; I start driving stop & go around town and over time engine heat makes its way up to the intake and warms it up. I get on the highway or a long road with a higher speed limit say ~45 mph and the intake actually gets cold AGAIN, I can pull off the road and the plenum is cold to the touch.

So what I want to do is make something to allow the intake to be heated from engine coolant. It's not a new idea, I know Ford did it with a lot of their production engines and it is actually a lot more efficient than using exhaust heat. What I want to do is make some small metal box or wide flat tubular device to somehow adhere to the bottom of the intake plenum and just route the heater outlet through it. Any ideas guys? Looking for max heat transfer while still being feasible, I don't have the equipment to prototype a billet aluminum part lol.

And before anyone says "get a regular RPM intake" again I'm running Magnum heads which have no provision for exhaust crossover even if there was an intake for Magnums which had it. And I don't want to use exhaust heat anyway.