Interesting. Back from my old competition days, this issue was that nothing may be permanently "affixed" to the motor. Adhesive tape was OK, but glue was not. I have heard that corking the motor works and is legal, and could even be done on the field. This is not cheating like corking a bat in baseball. Rather the booster motor is plugged by inserting a cork, like bottling wine. I have never done this, but I have bottled wine.
I have a cheap hand held wine corker. The corks are first soaked in water. the corker compresses the diameter of the cork and pushes it into the bottle. I doubt that a wet cork would be compatible with a BP motor. A more industrial corker might work better. Wine corks are one of the most expensive parts of home wine making and they are hard to find. Commercial wine bottling has mostly gone to screw closures and elastometric plugs that can be removed with a cork screw. I see no reason why a suitable elastometric plug and insertion tool could not work for plugging BP motors.
My approach would be to use a thin metal disk with a double sided tape gasket, and a very strong motor retention method.
