Just noticed copying a US char and EU char to same PTR just works fine :P
They never allowed this option on Live realms however. I rerolled as long ago as 2008, just interesting to see this right now even while it probably is in PTR for a long time now.
I got 2 accounts on the same bnet.
(mind you my inactive US account char is a level 20, under the Trial cap), the other chars have weird names with letters and numbers and cannot be copied.