How do you write a cross-staff arpeggio

I am transcribing a song by Poulenc. There is an arpeggio that flows into a sustained chord in the piano part that I don't know how to do the notation. Here is what it is supposed to look like:

It's a fairly common device and I have a feeling that, if I knew where to look, the solution would probably turn out to be quite simple. Any advice?