GM 3400 V6 thermostat replacement - how'd you get the rear bolt out?!

I'm getting some pretty erratic temeperature readings and no heat
whatsoever on my 97 Trans Sport Montana, so I think it's thermostat
time...

If you're not familiar, the thermostat housing on the 3400 is directly
below the throttle body and right smack next to the exhaust crossover
for the front manifold, leaving maybe 1/4" of clearance between the
side of the crossover and the head of the rear-er of the two bolts that
attach the housing to the block. It looks my best bet would be to get
at it from the rear with an open-ended wrench, but I still don't see
that bolt coming out with that pipe in the way.

I don't think I'll have much trouble with the front bolt, but
does anyone with 3100/3400 experience have any suggesstions for freeing
the rear bolt that don't involve removing the exhaust crossover?

Thanks a lot!
-Bryan