I've seen an interesting domestic hotrod part that is basically an electric inline coolant pump that fits into a hose. It pumps constantly, possibly varying speed based on temp. That would keep the coolant flowing well even when engine is idling.

For a similar part available in a junkyard you might try looking on a VR6 equipped VW. My Jetta has a supplementary coolant pump that operates on some unknown schedule. I guess cramming 6 cylinders into a head barely larger than a 4 cylinder's created some hot spots and it needs more coolant flow than the pump provides. It doesn't provide the full flow like the above hot rod pump thing, but might be enough.