I read a thread once where someone talked about jumping off the giant Combine spires and having a mage CotH her back on top while she was in free-fall.
Next time I'm on. I'm grabbing a mage and trying that...until it works.
In The Hive on the Living Bridges. If you fall off of them you fall into Stoneroot, kind of like jumping off of POS. VERY long fall hehe, got me doing the Slipgear quest.