About 20 years ago I worked in a lab making about 2,000 B&W custom prints a month with two D5's and a roller processor. For blown highlights I'd take the pre-flash diffuser I had made from the Ansel Adams design (two spaced pieces of translucent white plex/perspex, sized to slip a 75mm gel into the slot between them) and hold it against the enlarger lens. About 20% of the main exposure worked to increase highlight detail without fogging the paper. I left the negative in because I had to work quickly and it was more convenient if I needed to make a second print. One layer would have worked and given me shorter flash times, but I didn't need that extra speed and didn't want to take the pieces apart. I got the plex for free from the cut-off bin at the sales counter at Cadillac Plastics in Minneapolis.
I didn't test for before/after differences. Hopefully Les will chime in on that.
Lately I've been thinking about testing for the differences in flashing VC paper with blue and/or green light. I have some LEDs that should be coming on Monday so I can make myself a dimmable, switchable blue/green flashing box similar to the RH Designs flasher, running off it's own timer. There goes that patent out the window.
P.S. Any lawyers know if an APUG post qualifies as prior art?