They now do a compact, but it is still big. Doubt it will just fit where IS horn is.
I've got a twin air horn set up, adapted by previous owner to have compressor under the seat and one horn either side inside fairing. Even that is a tight fit. With air pressure, horn won't work over 100 mph, which does not affect me, but watch where the horns point if using air horns, should really be back and down.