A tip is to remember exactly where on the screen the buttons are. So you press record, join the bg, jump 2 times, klick on the spot where "LEave Battleground" is, then stop recording and just play that. Thats a loop of like 15 secs so if you miss the join first time it only takes 15 secs for the next join. Would work better imo.
This requires that you join from a BG NPC (otherwise you would join a new AV when you were in AV and you would never get any marks, though I don't know if u can join another AV when you are in av already :P)