I got an idea for a "from the bottom" temporary fix for the leak.
But I don't know if most people will be able to get it in place.

Esensually it will be the same as this plug with the head cut off.
with a tapped thru hole in the center.
A bolt will installed there and will be extended after the plug is put in place.
There isn't a whole lot of room to turn a wrench, but there wouldn't need to be major force to hold it in place.
I'm thinking Loctite on the thread and use a string to turn the bolt.
And when you're ready to do a proper repair you can pull it up from the top.