That's actually how a rear alignment is done on these cars.. Except most of the commercially available shims are plastic!
Where I used to work years ago, we got them directly from a Hunter Alignement Rep.. Most of them were a universal fit for a dozen different cars.. All they are is a plastic disk slightly thicker on one side.. There were llittle charts you would put them on that would tell you which way to install it to get the adjustment you needed.. Then there woudl be markings on the chart on where to cut out notches for the bolts to hold the spindle on.. I'm thinking it was a common Chrysler shim that fit VW's.. Might have even been for Horizon's/Omlettes...
Napa used to be able to get them.. I would imagine they still can, if you can find a parts monkey that knows what you're talking about.. We origianlly got them through napa till the local store closed.. The Omlette is just the red haired step cousin of the Rabbit family..