There was a thread on the Black and White forum on this. Another manufacturer (details in the link I posted) sells a mid length op rod for the WK. Member jiffx2781 installed the rod and a new barrel; in the thread they stated:
The manufacturer also has a rifle-length op-rod available.
I read on another forum that people have sealed the carbine port on an AR-15 and drilled a new mid-length length port, but I have no idea if that is safe or could cause a possible malfunction. Probably safer to get a fresh barrel to go with the op-rod, if the gas on the hand bothers you that much