It did work on 3 cars I know of some times had to push down on the belt with one hand and it worked to torque them to 12lbs personal experience
I have heard of people using a old belt wrapped around the clutch to then griped with vice grips to hold it
With the clutch engaged with jumper wires from radio shack.
But down here in Texas we don't get rust in everything
So maybe would take the old belt trick with vice grips clamping the belt to make it work in the rust belt states

And if the first and second trick fails
eBay item
Powerbuilt® A C Clutch Holder Tool 648980 | eBay
$18.95 free shipping

Glad you pointed that tool out! Auto Zone had that on the rental list too, so I picked one up last night. Bad news is that I spent over an hour this morning JUST trying to get a good angle on the compressor clutch to get the clutch'* center nut removed. Every centimeter of movement on the nut was like trying to move a seated elephant with toothpick (i.e. barely moving)! The threads were apparently so rusty that I eventually gave up for fear I would snap something in two and really be in a bad spot. I used PB Blaster and a wire brush as far in as it would go, but it didn't seem to accomplish much.

I put everything back together and drove the LeSabre to work today. The clutch noise is gone now anyway, so I'll see if/when it returns (and will keep watching for more new metal shavings, as I cleaned up the others) and go from there. Maybe I can find a shop that will just back out the clutch plate a few millimeters and see how that goes, if it ever ends up being needed.