Thank you for writing.
Currently, the RadPropertyGrid can only work with editors shown as dialog. Your scenario, though, is perfectly valid and I have added a feature request for this case in out Public Issue Tracking System - PITS. You can use the following link
to navigate to the PITS Feature and add your vote or comment for it.
I have also updated your Telerik points for the good suggestion.
Should you have further questions do not hesitate to write back.
the Telerik team