Hi Ian,
There is not currently a "split at X note" command for the staff (it is on the "to do/wish list").
One "sneak technique" that has worked for this type of thing for organists (who split out such notes) is to use the "Staff/Split Drums" on the staff (yes, you read that correctly
) and then re-merge staves based on the note placement. Odd, but true.
ttfn,
Sherry