Two suggestions:
1. As Kitcat stated run your auxilary radiator full blast - an old trick we used to use with tow vehicles
2. Can you fabricate a "cold air box" to encapsulate the turbo then, similar to race car brakes' duct air thru the box and exit thru either a side vent or under the car?
We used to use the cold air box, more of a forced induction, on an e-production MGB. I would think you could use the same concept todissipate the turbo heat.
Another related option would be to seal against a set of hood louvers, similar to how the heater air intake seals against the hood, from the cold air box.