I need to have part only of a bar notated with free rhythm. Also other staves need to be synchronised. I've tried using \cadenzaOn but then I get a barcheck problem and the next bar goes odd. I can't see anything about this in the snippets or manuals. A minimal example follows.
There seem to be two issues:
1) How do I get the desired result, which is one bar with the first 2 crotchets synchronised with the bass, and the rest unsynchronised?
2) This isn't in the example, but what if I want a free section within a bar, but synchronised accompaniment at the beginning and end of the bar (e.g. a chord on the final note of a cadenza).