Pre-flashing works with any exposure-sensitive material including film. For film one is concerned with shadow information, whereas with paper its highlight area information.
For film I use a white-balance filter (as described in Lambrecht's "Way Beyond Monochrome")
For fiber-based enlarging paper I use a flasher by RHDesign. It easily installs on the enlarger lensboard.
For silver chloride contact paper I use Besseler Audible timers that give control to 1/10 second. I pre-flash the paper prior to placing in contact printing frame.