We have an '05 Passat TDI that doesn't have a block heater provision. One of the 'stick-on' heaters I looked at req'd the paint on the pan to be sanded down to bare metal. I didn't like that idea but I guess if it was removed, it could be repainted.

A custom circulation heater is available, but I haven't made a move on one. Zerostart makes the base heater, but they don't show an application for the 6.0L. Probably because they are all supplied with the block heater, and the cord is available . (if it's not already installed)

Take Care