placing dynamic where no note

I would like to place a dynamic marking at the end of a diminuendo hairpin where there is no note, but I want the musician to know that they must decrease to pp. (see attached). I can't figure out how to do that. I select the note and choose pp then try to click/drag it to the right of the diminuendo but it stays to the left and the diminuendo shrinks. thanks for any help.