Fan fret could help in the tempering but might just move the problem along.

I increasingly use my carbon fibre Rainsong for dropped tunings as the neck will not move at all, and have found Martin 12.5 strings to be of benefit. If I put 13s on, I can drop the whole thing to baritone BEADF#B without wobble, but less volume than my baritone Alvarez.

Neck movement is, according to George Lowden, a huge contributing factor in tempering issues with dropped tunings.