Hey strarup.... very nice work.. I see you are getting familiar with CPS. You were right, I had a older version of CPS, so I have updated to version 3.5 like youself ;-)
Actually version 3.5 have a mirror/stitch tool itself, so you wont have to use the method i showed you. Just remember to uncheck "keep border" for the best result.
By this way you dont have to move pivot and mirror an instance.
If you by some reason want to do the mirror yourself, there is already a tut about it here: http://www.3dcentral.com/tut1.html
PS. strarup: if you dont have it allready, you need to get MJPolyTools at www.maya3d.dk
Looking forward to see more of your work