Beginning in the 12.2(33)SXI4 software release, Quad-Sup Uplink Forwarding is supported which allows for a redundant supervisor to fully boot Cisco IOS Software, thereby providing a deterministic recovery option for redundant supervisors in a VSS chassis.
Refer to:
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps9336/white_paper_c11_429338.pdf
