Making thumbnails

I have downloaded GGSE_V2 objects from the net, but they're just named GGSE001,002,003 etc and have a user GUID, but no thumbnails. In the Library Object Manager, it's possible to find thumbnail (from now on FT) or create new thumbnail.(CNT) But as I don't have the thumbnails, I can't use the Find TN option, and if I wanna use the CNT, do I have to insert them 1 by 1 in a scenery, compile and open P3D to see whhat it is and take a screenshot of it?
Surely there must be an easier way, if not with ADE, maybe some other prg. can do it?
Since Instant Scenry 3 doesn't work with P3Dv4, ADE has become my tool for placing objects, even though it's a bit difficult sometimes as you can't see the result in P3D at the same time as in IS3.

Regards Jorn.
MCX has a "Save preview file" icon which creates a .bmp file. Then, in ADE, use Library Object manager and Find Thumbnail to put preview picture into ADE library.