Conditional Statement to Detect Mounted State

I'm wondering if it is possible with a command line script to set actions based on whether you are mounted or not? The problem is that if you are mounted, and you give the all kill command to a loose pet, the pet you are mounted on will refuse the command and lose loyalty.

What I want is a conditional statement that will say "[pet name] kill" if I am mounted and "all kill" if I am not. It seems to me that this would be possible, I just don't know how to do it.