Hey, I have never tried anything like this before, but three obvious ideas came to mind, Im sure you already thought of them butjust in case, here are my thought.
1.First would be to hang it from something with clear fishing line or something even less noticable. You could hang it from the ceiling, or better would be hanging it from a higher point on the diorama, for example if it was flying under a bridge or something, although thats not likely.
2. I personally dont like this idea, but you could make a thin hardly noticable clear stand out of plastic that the plane would rest on top of.
3. In my opinion this would look the most realistic. I would position the aircraft so that some tiny part of it, like a wingtip, is touching the tip of a tall tree or something, then glue it. Still it wouldnt look perfectly realistic, but much better than hanging it.
Hope this helped, Ian
"Scanlon: work your knobby hands on the table in front of you, constructing a make-beleive bomb to blow up a make-beleive world."