Ahhh....
depending on how many flying models (one? two? three dozen?) I would just try to build something consistent with the base theme of the army.
For example, if urban rubble, go with a partically ruined wall, or a twisted girder sticking out a a pile of debris.
For a desert theme, a piece of standing stone, or rocky outcrop.
For industrial, a bent pipe, or piece of wreckage.
Could also use an old column, or sign post, or tree etc.
All depends on the base theme of the army.
Of course, this may not be very efficient depending on how many you have to make. I do custom scenic bases for all of my bigger models...and have to admit, that at times it stretches my creativity when coming up with new ideas.
best of luck!
Automatically Appended Next Post: Here is an example of a flying stand incorporated into a base design...
http://40khobbyblog.blogspot.com/2013/05/custom-resin-flying-base.html
However, like I said, this might be a bit much depending on how many you need...