You can have cross-staff beaming on split tracks.
Select the note(s) in the bass staff you want to have connected to notes in the treble staff, choose Staff from the edit menu and then select Crossed from the submenu. (Only notes that are beamed together can be crossed.) When you want to do cross-staff beaming, make sure you only select notes on one staff, not both. If you choose notes on both staves, the crossing effect will cancel itself out.