It takes me less than 30 seconds to position the brushes so I can slip the armature into place, and they hold themselves back until I'm ready to release them. It's a trick I learned in the late 1950's and it's worked ever since. All it takes is a short ring of exhaust tubing just a bit larger than the diameter of the armature. A piece of PVC pipe would also work well, most likely.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!