Bill its possible because all of the servo port traces for the power leads (positive and ground) are connected internally, it makes no differance where you imput the power. The reason it is done is to minimise the weight and size of the extra plug to allow such a small and neat little Rx.

I suspect this is common to many larger units also even with the extra ports. I have about eight or ten of the little jewels (hard to keep count) and use the 555's almost exclusively for pylon racing.

John