When you want to make text appear directly at the center of titlebar (not just between left and right elements), it may be necessary to set high "Pad" value. This will work, but large text will run out of space quickly and will be cut in one of corners, while the other still have plenty of space available for text.

Take a look at this: http://i25.tinypic.com/21oojv8.jpg

"Lista...ych" is pidgin's contact list, which text has been cut. But it has much space on the left side. I think it would be nice, if text would be pushed to the left, instead of cutting it. Maybe doing something like "double Pad" would work? First pad would adjust position of text while the second Pad would make sure that text will not step beyond some area (so it would be "tolerant Pad" and "absolute Pad").