Mark, the air line idea may be something to follow up on, but may not be precise enough to satify FMCSA.  They do have the lift axle situation covered.  Here is the way that § ends:

 ". . .This paragraph shall not be construed to prohibit-- (1)  Devices that could exhaust air from both axle systems simutaneously; or (2)  Lift axles on multi-axle units."

My situation is that this is not a "lift" axle, merely a spread axle that eats tires badly if you don't dump the pressure on that back axle when making tight turns, such as on a paved lot.  It also helps when turning in a field.  It is okay to have the manually operated valve but it cannot be accessible from the cab; I don't see their reasoning.