Maybe have the 0 wounds only make him take a crit but keep standing? And indeed keep standing until it's minus his wounds amount, then knocked out, all the while still taking crits by taking a hit while below wound threshold.
Give him 2 separate rolls/rounds of initiative perhaps.
Make him burn through destiny points to downgrade their attacks.
Don't allow players to burn a destiny point in return of same roll unless they spend 1 extra (cumulative stacking each back and forth).
Keep the environment moving and working against them, like Maul with the energy barriers. Use destiny to justify it if you must.