Another option is to remove the motor from being mounted on the stand and to hang off of a wooden vertical platform.
Sort of like a big and wide sliding dovetail made out of plywood. Motor is mounted on the moving part, with the keys on the stationery part starting just a bit higher than the length of the motor platform. This allows the motor platform to be placed under the keys and then lifted up into position.
The weight of the motor provides the tension for the belt. Secure the vertical platform to the stand via some bracing. This would only be good for smaller motors =< 1.5 HP.
Depending on the clearance inside the stand, you might be able to move the motor over laterally to put the pulley on as per the instruction booklet.
Dropped the decibels here from *having* to wear ear protection, to
*not necessary* anymore (but still do because other stuff is running).
YMMV