Sundown,
In a purely technical world you could do that. However, I would almost guarantee that your company procedures or authority approvals, whatever form that might be in, will disapprove. The last thing anybody wants you doing at 500 feet is changing bugs, etc. Further, a fail-passive approach has different ground equipment requirements, in terms of touchdown zone lighting, RVR values, etc. It is certainly possible that all of those criteria are satisfied, and you could in theory brief the approach for the contingency you have suggested...but everyone I have worked with prefers the idea that when it drops out of LAND 3, you go around, assess, re-brief, and fly the fail-passive approach with LAND 2.
Assuming of course that you have enough gas and that the guy having the heart attack says he can last another 20 minutes...