I'd say an A/B box would be easiest, to split between the input of the amp and the input of the POD, then either run the POD to the effects return or direct to a PA, though, this method requires that plugging into the effects return and leaving the effects loop on won't turn off the amp's pre-amp from the signal path (so, most likely, a parallel effects loop is needed).
The other option, and really this might be even easier, is to plug it in the same way as above, but using a serial effects loop that's footswitchable, and splitting the guitar's signal to both inputs all the time. This way, if the effects loop is off, you're getting the head's pre-amp, and if the effects loop is on, you're getting the POD :yesway: