I don't know if it would work, but you would need to make the spacers 3mm. The distance of the 2mm spacer ring & the second gasket adds up to 2.5mm, plus the thickness of the original gasket that would no longer be used, comes to 3mm.
At least, half a mill is the measured thickness of the two new [uncomperessed] gaskets here on my desk.


Would you really want to risk it?
Surely someone somewhere can make a copy of a standard diff gasket in 2mm alloy or steel.
I am attempting to source a Pitroad ring, mainly for the purpose of finding the "actual" thickness. I'm sure that 2mm is the go, but i want to make absolutely sure.

Which car is this for?