Thanks to Bert and Kim for the suggestions . Actually, I was not looking for a way to pause the script, but to slow down the animation. Bert's suggestion about changing the tick rate on the "script clock" was a revelation. Who knew? (obviously not me).
Well, in the powerful ideas book this technique is shown in project 6 (page 32 in the english version). Even if you're not using it in class it's really worthwhile to get a copy and run these projects for your own education.
Cheers, - Andreas