Based on the suggestion I picked up a CF card with an CF to IDE adapter.
For the first tests I took the cheapest card and adapter I could get. And they work perfectly.
The adapter has to be configured as "Master" and the card has to be formatted as FAT16. This limits the maximum capacity to somewhere around 4GB.
I've added a picture of the result to the photo album of this group.
The next step is to get one of those adapters in the formfactor of a 2.5" hdd and maybe a more professional card. This will the modification more easily.
I'll post the progress here and on tekwiki.