The Starn twins just had a show of work in Cincinnati where the work was lit by an arc light that faded the prints through intense UV over the month of display. Viewers had to wear eye protection and were offered sunscreen at the door.

Commercially, there was a machine we printed with called a stabilizer processor. It developed the print with a concentrated developer solution, then "stabilized" the print with a second solution. It worked like a fixer, but only temporarily. Under display, it would darken to obscurity. I believe Adorama still sells this stuff, so you might be able to get some and use it in place of fixer.