MS3 Cupped Tires from Uneven weight distribution

[Overspent]

I'm about to buy my THIRD set of tires for a 2009 MS3 with 40K miles. My tire place tells me the cause of my "severely cupped" tires is that too much of the car's weight is up-front, allowing the read wheels to "skip" off the pavement- the cupping happens when they return to the ground.

I don't drive the car hard (much), and the tire have been rotated regularly. I did yank-out the spare tire to make room for a sub, amp, and sound processor. I have also put maybe 15 lbs of Dynamat in it, pretty-evenly distributed fornt-to-back.

The dealer acknowledged that weight distribution was the probem. I said: "so it's a badly-designed car..." Of course the dealer blames my troubles on my sound system and D-mat.

So I'm wondering if anyone else has encountered the "cupped" rear tires issue, and what any of you would say about how to fix it (short of putting 180 lbs of sand in my tiny cargo area (the dealer's suggestion).

Thanks for any thoughts -