Why?
Don't you own the inside? Even if you don't, you should be able to
get permission to get access and remove some drywall and have free
access to both sides for a very short period of time.

A litle drywall and paint and it looks better than new.

It's not drywall -- it's tongue and groove knotty cedar -- extremely hard to
remove without damaging (I've tried in the past), and it would be almost
impossible to match the rest of the room if I replaced it.

I'm actually about halfway through the plan I outlined earlier -- supported
the above structure with jacks (there seems to be very little dead weight on
the section anyway), and cut out the bad stuff. I've shored up the short
wall and replaced the sections of the top plate, with several new studs to
make sure it's all rock solid. Now I"m inside for a few minutes cooling off
before I do the joist itself.

Wish me luck!

-Tim