If it's about 802.3af PoE compliant approach...

Above statement is for DIY modification on existing Ethernet dock (e.g., adding a RT9400 module and a large capacitor.)
This does not preclude a new design with factory built-in PoE capability nor
a separate PoE adapter module in front of the Ethernet dock.

There is also an ad-hoc, non-standard approach using pairs 4+5 and 7+8.

In all cases, the PoE supply voltage needs to be pretty high such that the instantaneous power demand (over the long and thin Ethernet cable ) from O2 will be less susceptible to cause the power-dip/brown-out condition and then hang the O2.