Depends on what your permit says. They have quotas for different areas in Yosemite. My walk-in permit was for Little Yosemite, so even though i didn’t plan on staying there, i did. It worked out just fine.
If your permit says you have to go past Little Yosemite, you can pretty much stick to your Half Dome plan anyway. Just do like Weez said, and camp past the Half Dome junction. There are plenty of flat sites near water. Only problem is that’s a big time bear problem area, so you’d better have a canister, EVERYthing with any smell out of the tent, and either nerves of steel plus earlplugs -or- pots and whistles of steel and the love of staying up late at night scaring away bears. Personally, i’d hope for the the Little Yosemite permit. The rangers try to keep bears clear of that camping area, plus their’s a toilet. You’ll have plenty of “authentic” camping later in the trail.
markv