I just upgraded my Nanostation M5 to BBHN, but the second Ethernet PoE is not enabled.  Does anyone have a trick to turning this on?  If not, how can I get word to the developers about this?

This is known and at the moment isn't high on the list to be enabled due to lack of good limits notice and a previous issue in 2011 where we know some hardware out there and avaliable may have flaws untill we learn for sure these are not current issues

https://forum.openwrt.org/viewtopic.php?id=23442

You can try the procedure here AT YOUR OWN RISK

http://wiki.openwrt.org/toh/ubiquiti/nanostationm5#poe.passtrough

Ubiquiti gives very little info about this port, from what they do give it's meant to run a CAMERA not a full 2nd node so keep that in mind.  I've read posts of these ports being fried by users in the field.  Make sure if you do use it your using 24v 1amp supply to be sure current through the port is at a minimal and reduce risk of frying the port.