Thank you very much for your reply. I have added the script and it works.
I know there are a lot of script fragments on the Eviware site and also on the internet. A developer was kind enough to help me out, but for a tester as me the proces of scripting is possibly a bit too complicated. It would be very nice to be able to add a datasource to a mockservice in the same way you do when working in a testsuite. Is it possible to add this to the wish list?