This is my mostly-done layout importer program for gmb.
All you do is run it and select the desired .layout file and it will copy it to the right directory for gmb to see it (~/.config/gmusicbrowser/layouts).
Right now, gmb must be restarted for it to see the new layout file.
The future plan is to integrate it into gmusicbrowser and make use of a "refresh layout list" that squentin is planning.
If you are into testing, you can use an argument to it so that the destination folder is ~/.config/$argument/layouts. $argument defaults to gmusicbrowser if no argument is given.
The code can be seen here: http://paste.pocoo.org/show/337858/
Some screenshots so that you guys know what I mean: