I have created a script to do this until (if?) we get this added to MC. This is in no way associated with MC or Billy.
This script will do two things.
1) It will make sure your TV show season folders are in two digit format, if not it will rename them.
2) It will copy each seasonXX.tbn file in the shows root folder to the appropriate season folder as folder.jpg.
*Note: You Have the option to have it replace only with newer files, for the first run I recommend you say NO and let it replace them all, this will ensure your folder.jpg's are the same as what you see in MC.
Created with autoit if anyone would like to de-compile it and see what it does / or test for anything dangerous.
Warning: I made this program for my own use and am only sharing it in case someone else would find it useful. As such I offer no warranties, and am not responciple if thie script ruins your collection, gives your dog herpes, or anything else.
Tested with server 2008 with several hundred TV show folders.