Notes from 2 or more Staves on a Single Staff

The image describes it better, but what I was hoping to achieve is to have the notes from 2 staves written on the same staff. I tried it, but musescore will not let me -- for the obvious reason that the notes do not fit the time signature.

In the image -- the top 2 staves combined is the original treble staff, while the bottom 2 staves, bass.