I wanted Bistro UI in the BLF D80, so I soldered a 17mm driver from Mountain Electronics onto the top of the retaining ring. One of my lights has the long tube and I use unprotected cells so there was a tiny bit of room to spare.
I posted my ugly method in the “What did you mod today?” thread, then DEL pointed out that a 17mm driver will indeed stay put under the D80 retaining ring.
I tried DEL’s suggestion and it worked. Both of my D80s now run Bistro UI and have no visible PWM! :+1:
That’s my ugly mod on the left, and the “correct” way on the right. 
For more info, start here at my post in the “What did you mod today?” thread. Hope this helps!