Preseed create two empty partitions ("do not use") with partman

Question

I have a question about preseeding. I need to create a simple partition table like this:

/    10 G EXT3         primary       
swap 8  G SWAP         primary
     100G "Do not use" primary (to be later used for DRBD)
     100G "Do not use" primary (to be later used for DRBD)

The first two are no problem but i cant find the correct way to create two empty partitions of 100G which i can use for DRBD.

Is there someone that can give me a hint?

Thanks alot! Remco