iporter said:

I tried enabling teasers and applying a fixed teaser message, but this resulted in restricted pages being displayed in the navigation to all users (actually, this also resulted in displaying the content to all users - I had to use the is_teaser() template tag, is this normal?).

No, the part about displaying teased content to all users is not normal. I have to suspect there's something unusual in your template code and would have to see that to recommend any workaround.

If you can get that straightened out, reinstate the Teaser settings, download the updated Role Scoper Development Snapshot, and add this to your wp-config.php:

define( 'SCOPER_TEASER_HIDE_PAGE_LISTING', true );