There is also a route that takes off from Lower Boy Scout lake. Start at Whitney Portal and climb to the North Fork of Lone Pine Creek. From here ascend the mountaineers route up to Lower Boy Scout. There are some easy to follow class 2 skree/boulders as well as many class 3 variations along this face.
Just climbed Thor Peak starting from the North Fork of Lone Pine Creek. There is a sign posted just after you turn off the main Mt. Whitney Trail onto the North Fork of Lone Pine Creek Trail. The sign says that you need a permit even for day hiking if your are going to continue past Lower Boy Scout Lake or anywhere in the Whitney Zone. Thor Peak is squarely in the middle of the Whitney Zone. The ranger I ran into was just going to give me a warning for not having a permit, but didn't give me anything after I told him I didn't really go "past" LBSL. But, I was in the Whitney Zone, so he could have given me a citation.