Not sure how I'll manage to balance them upright but I'll see what I can do.
Purchased the extended GSM battery from a Korean eBay seller ( Korean gnex is shipping with the extended battery so I imagine that's how the seller obtained them). "Shimshop" is the eBay seller name if I recall correctly. It works just like the LTE extended battery and back cover in that it basically fills in the hump at the bottom. I can say even with out my wife's phone in front of me that the GSM version maintains the same thickness difference compared to the LTE version also with the extended battery
I think a better idea is to lay one phone down on top of the other. For example, place phone one down on the table on it's back. Then lay the second phone (again on it's back) on top of the 1st phone's screen - if that doesn't work maybe try laying them face to face. Then, use something like 2 books to make sure the tops/bottoms are lined up. Then snap a pic of the pin alignment.
If you try standing them up, and one of them is not level, it's going to throw off the alignment.