Allow choosing where to put unfinished issues

When closing a sprint, any unfinished tasks are moved to 'the top of backlog' according to the dialog, but in fact they end up in the first not-started sprint. Since we have multiple teams working on overlapping projects, we regularly have sprints from team A showing on the board of team B. When this happens, any unfinished tasks from team A may end up in a not-started sprint from team B.

It would be very nice if instead of automatically putting the unfinished tasks in some sprint, we could choose where to put them (possibly including the actual backlog). This doesn't have to be per issue, I just want to specify where the whole lot goes...