I don’t think Ionic supports this at the moment, unfortunately.
The underlying issue is that the library that Ionic uses for ion-content and ion-scroll, the Zynga scroller, doesn’t support elements being ‘sticky’. This makes a number of things like sticky list headers not trivial to do.
I know the team is working on said sticky list headers, and I’m guessing that once those are in place, the groundwork will be there to make feature requests like yours easier to do.