show key change at D.S.

Following situation:
The music at the D.S. is in B-flat. The Coda (Trio) starts in A-flat, but the place, where the segno is, is in E-flat. Therefore I would like to show a cautionary key change to E-flat at the D.S.
Any suggestions, how to achieve this?

I believe Leo had a solution for this. Something like adding an infinitesimally small bar at the end, hiding the rests, and changing the key there.