I would think that it would be fairly easy to just create an oil pump run-on circuit with a timer for such an issue. If your oil pump is electric, or can be converted to electric, you could just make a system that let the oil circulate in the sump, through the turbo, and not even be idling. That would prevent coking and cost no fuel, best of both worlds. It would run off battery power after you shut down the engine. Just throwing ideas out there, I know some of them might not be cost effective.
EDIT: I just Googled this and came up with a website that does this specifically. They use this application for race engines to prevent coking. The Prices aren't that bad in my opinion, though it might cost about $300 or so for a setup that fits you. Check it out:
RBRacing