Thats a cool idea, the MV Agusta uses the ignition switch to "switch" to different preset Fuel Injection Maps. It onlt works when the Engine it running.
I am sure it can be done, HOW, I am not sure.
I assume you would have to mount the actual door opener to somewhere on the bike, splice the power line that goes to the horn and run a wire to the device's trigger.
Or just get velcro and attach it somewhere, maybe you can get an aftermarket device that is slimmer?
Let us know what you find =)