The "Why Do I Need a Bear Canister?" section on:
http://www.fs.fed.us/r5/inyo/recreation/wild/faq.htmlsays nothing about the MR, but does mention by name the Main Whitney Trail.
While it appears from reading that section that bear canisters may not specifically be required on the MR, I'm gonna bet that the same "smart" Whitney bears that have learned how to overcome the counterbalancing method at campsites on the Main Whitney Trail probably don't lose that knowledge when they wander a few hundred yards to the north in search of food at similar MR campsites. But if you're willing to risk your entire food supply....