Extend stems beyond beam?

[Henrik Frisk]

Having just started using lilypond I came across a problem I can't solve. I am 
writing for harp and I have a lot of cross staff notes. At a few places I wish 
to notate a chord with one note in the lower staff and one note in the upper 
staff. I have figured out how to do this as long as the chord is not beamed 
with a previous or following note. Simply put, what i want to work out is how 
to extend a single stem in a beamed group of notes beyond the beam in order to 
connect it to a note in the other staff.

This may sound like a silly thing to do and I don't necessarily need to do it. 
But I still want to figure out if, and then how this can be done.

Greatful for any suggestions,

Henrik Frisk