I've got an PODxtLive too and I don't think there is a talk box effect per se'
I used to have a Digitech RP2000 that had an auto-wah preset that could kinda pass for a talkbox.
There's an auto-wah on the XTL . . . maybe that could be tweaked into something similar.
I don't know for sure, but I wish I could help you out.
Good luck man!!
If you're successful please post the tone if you can. I'd like to have a talker too.