In regards to using a Rotary scrubbing ("Mechanical action") one could use the small dual 6" (each brush dia.) inexpensive machines. They work great and would not have over spray.
Mr. Good Wrench (Jim Morrow) has experience using that system. In fact, I remember giving him the contact years ago.
Hope he comments.
The JAGUAR MX-2 ETM @ cross-american.com