How to customize the starting position in an Engine Match in the Fritz 13 interface?

Hello.

I just bought Houdini 3 Pro with the Fritz 13 interface, and I also have Fritz 12.
I was wondering if it was possible to customize the starting position in an "Engine Match"?
http://img838.imageshack.us/img838/8933/enginematch.png
Surely there must be a way, but I can't find it..

Thanks in advance.