A HO might actually work, since a good P38 pilot will be trying to dive under you.
A HO against a poorer (or braver) P38 pilot will get you killed, pretty much only a 110 has the gun package to face down the P38's concentrated guns and live. (Although that spinner cannon is nothing to sneeze at.)
The P38 can't climb as well as the G10 (which hurts the P38, since that's usually its strongest point), so your spiral climb should work just fine. If you're having trouble with the other plane cutting you off, then you're making your loops too tight. As I said, the P38's climb is usually the strongest feature in a dogfight, so it's unlikely a dedicated stick (like myself) would notice they were being led into a trap.
If you're at a super-high alt, you can always dive and get them to compress at around 500mph, at which point any turns you make --if they can follow at all-- will cause them to black out. Then you've got the upper hand.