nah people have mounted air horns in the stock location. the compressor's not that big. a little smaller than the evap canister if i remember correctly.

i think there's some add-ons that creates extra channels from your alarm. it does this by interperting 2 quick pulses as one channel and one pulse as separate channel etc. idk if you'd still be able to get different outputs though (latched/timed/validity). something to look into though if you don't want a second remote. it might make operating the separate channels with your alarm remote a little complicated though.

-marc