force flat beam in piano staff that uses \autochange

[Michael Winter]

Dear All,

I have a piano staff that is using \autochange. The notes are just running 
16ths throughout. In a beamed group, sometimes the notes are all in the upper 
staff, sometimes they are all in the lower staff, and sometimes they are in 
both. What I really want to do is force the beam to be flat and centered 
between the two staves. Is this possible?

Many thanks in advance,

Mike