LED light bars are intriguing. From 4" to 50" wide with options of flood, spot or in-between lenses or even combinations of the lens types, single or double row. Mounting one across the front of an FJR would seem to require some creativity for sure. Best bet you would still need to use the mirror mounts to attach to. Either two individual brackets or some sort of spanning bridge depending on how the light bar mounts (though a small LED bar is pretty light and compact and perhaps could be mounted through the plastic with backing plates if you don't mind ugly holes in the fairing).
My most rewarding farkle project was adding 4 Hella projector beam headlight pods as my aux. lights. Since no mounting brackets existed, I had to design and make them from scratch ( 6061 T-6 Alum.) to attach them to the mirror mounting brackets. Used mostly hand tools but did take advantage of a Bridgeport at work to mill a couple features. No welding needed. Probably put about 30 hours into the project but really enjoyed it.