[Overdriven]

If you're going to have a fan on the esc, have it blow into the alum pipes, simpliest and probably most effective. Careful wire routing would be required for this to be most effective. Removing the shrink will probably help a little too, and I wouldn't think it would void the warranty unless you solder on it. Besides, wouldn't running it in a land vehicle without the water cooling void it because it's not being run within it's design constraints?

On the more radical side I'm curious how effective a heat pipe system would be. It's what almost all pc cpu coolers are going to now. But that'll definitely void the warranty, and the aluminium pipe don't dissipate heat as well as the copper ones used in cpu coolers.