I don't have FSX so this is a shot in the dark (cue pink panther music). In FS9 to prevent AI aircraft showing up on the selection menu you could edit the .air file for the aircraft involved with AirEd (or similar) to change the behaviour. Record 105 of the file is the key. Normal aircraft have an entry of 0, helicopters = 1 and Non-flyables = 2. The AirEd info state this is for 'CFS AI Only' but it works in FS9 as well. I imagine that record still exists in FSX so you might want to give it a try - make a backup of the .air file first.
Nigel²
Edit:
Ah, I see Darren beat me to the punch, but looks like my shot (in the dark) hit its mark!