Cross staff lines

In barbershop, it's customary to use a dashed line to indicate a change in who has the melody. To change within a staff (lead to tenor, f.e.) it's no problem. However, when trying to move cross-staff (lead to bass) I can't make the line anchor to both notes. I can attach it to one end, but dragging the handle to the other staff just move the staves further apart. I didn't see anything in the manual or in properties that might allow it.

Any help or suggestions greatly appreciated.

Thanks!