Lowpuller,
Yes! That sounds like what I was visualizing, and 4-1 purchase should do the job for sure! I thought 2-1 would be sufficient.

But if the "righting bag" was a lightweight parachute-type material (sea anchor), it could be left attached to the righting line permanently (in a little pouch), so you could use it or not, depending upon whether you needed it.

And I am going one step further. If you need it as a sea anchor, you would leave the righting line attached where it is (base of mast or main beam)and run it through something up at the bows and deploy the sea anchor out of its pouch.

Just thinking out loud.