Hi Roncanator,
thanks (everybody!) for the responses.
I've experimented already with your suggestion,
but it doesn't work out very well, since the cheese slopes don't give room for the needed curve in the rails.
The overall result is then that there are nasty obstacles on the rails (try to glide off... ouch!)
In the plate 1x4 version of the Pet Shop though it works.
Then again the rails don't give enough room for a minifig to ascend or descend the stairs,
so you should make the stairs based on a 1x6 plate scale. The result then is very nice.
I'll make some pictures later to show what I mean.