To beat pig josh all you need to do is jump on to the roof that Jack is on and get on top of little shack thing. After that you will have a perfect view of Josh. If he tries to come up the stairs he will most likely blow himself out of the shack leaving him vulnerable for attack.

I found another way to beat Pig Josh. He runs a set pattern, but if you kneel down he loses you completely and goes back into creep mode. Jump to the lone tower(the one that fatboy shoots at you from), and stand there. When Pig Josh tries to blow you up, just jump at the right time and he'll blow himself to hell, but you will be unscathed, land and hit Hoghead in the back...and the rest is history.