I don't think there are any accessible boondocking areas close to the lake... might find something north of Truckee or on the Nevada side in a National Forest. You would want to contact the ranger station for the Lake Tahoe Basin Management Unit at:
Lake Tahoe Basin Mgt Unit - Home to find out what is available. There are some very nice campgrounds that are National Forest Campgrounds, one near Tahoe City, just south at "Sunnyside" and another right near the beach at Tahoe City. Very crowded sometimes. There are others around the lake...