Not answering your question, but...
... a buddy and I did a version of the Isolation and ended up at the south end. It took us a total of about 5 minutes to secure a ride (i.e. "hitchhike") to the north end at Colonial Creek. I bet this time of year you'll easily find someone to give you a ride.
BTW it took us two legs: one to Marblemount (first ride was west bound) and then another eastbound along HWY20 to Colonial Creek.