From the Strobist Flickr group:
"I just called the pocketwizard company and I was told that I could plug both strobes into the same pocketwizard using TWO cables because there is Two inputs on the PlusII.
So for all of you that did not know it, just like me.
Plug 1 strobe into the input on the pocket wizard that says FLASH, and then plug the second strobe into the second input that says, CAMERA FLASH.
Once you fire, both will go off."
http://www.flickr.com/groups/strobist/discuss/72157607702743864/?search=1+pocketwizard+two+strobes