I would not say that it's possible to group several items without starting to modify the underlying parts, which you don't want to do. I would really question if pulling in that many items into a content area is the right way to go. Perhaps add another layer, for instance a block with a content area where you can put all items for a specific visitor group, pull in that block and personalize it. That way you get a bit clearer separation and overview of what's seen for a specific role. Of course, I hope that this is a rare case and not something that will occur all over the site, then I think you would be in trouble.
The documentation for personalizing content in an content area states the following:
Is it possible to override the behavior for [Visitor group name] so I can group many blocks with the same visitor group inside the same group? Now only the fist block is shown.
I am developing a site for customer that is going to use 20 visitor groups and for each visitor group they want to show 4-5 different blocks. If they have to have 80-100 groups inside one content area it will be very difficult to use.