Unpitched rhythm notation

Hi, I’m wanting to write a specific rhythm (in Dorico) for a piano player, but without specific pitch, so they can play their own chord voicings - can’t find how to do this. Can anyone help please?

Rhythmic (slash) notation is added in a voice similar to normal up stem or down stem voices.
To create a new slash voice, enter notation input, then hit shift+alt+V.
The manual page is here.

Many thanks - sorted!