Well, I ordered some copper shims in 0.3mm and 0.5mm.
Probably I will only use the 0.3mm and even sand it down more.
Search ebay for number 172198719962 and 252331512658 - You will see on the pictures the (supposedly original), old thermalpads which do not seem that thick. With my n.a.k.e.d eye, it seems it would also be possible to use just thermal paste without loosing too much pressure on the dies.
I will report more, as soon as I have reveived the copper shims and took apart my notebook.