Considering that Superman was unable to lift mjolnir in JLA/Avengers,
Thor in Superman's uses his new found super speed to take away mjolnir, which superman in thor's body is unable to lift. Thor in Superman's body then beats the crap out of Superman in Thor's body.
After he's done with the battle, he visits Beta Ray Bill to borrow his hammer, stamps Beta Ray Bill's hammer on the ground, and becomes Thor again.
Better than that, while stated than Supes can pick Mjolnir, nobody says Thor in Superman's body cant pick it, so he still fetches the hammer in superspeed and proceeds to rape Clark.