We have chains like Sullivan Tire, etc here that are extremely knowledgeable on general alignment, have top notch equipment and understand the specs, etc. But I certainly agree they likely have little or NO experience with our cars.
The slotted shims are a great idea.
So my thought is to have them do all the measurements, set the Toe-In, and issue their report on the caster and camber. The proper slotted shims could them be purchased, and the calculations made, and the shims easily installed in the driveway. Weight of 200 pounds in both front seats I think is specified. Would have to bring along sandbags or something.