Hey guys.
I wrote a little Program in C# which takes care of the xml editing needed to implement trailers.
Basically it checks every sub-folder of a given path for mymovies.xml and inserts the Trailer Tags.
The Program will only edit your XML file if a trailer.mov is found. Obviously all trailers need to be called trailer.mov and be placed inside the Movie folder.
You can start the Program directly from inside your collection directly or you can supply a working path when you execute it.
Here's the link:
http://www.lasergunspewpew.de/trailerxml.rar
BTW:
It worked perfect for me but I hacked this together in like 10mins and it's just supposed to be a temporary solution until this gets properly implemented in MediaBrowser.