[racket] custom port question

I'm trying to build an output port that acts like 'tee', wrapping two
(or more) output ports and duplicating writes to them. This requires
make-output-port
(http://docs.racket-lang.org/reference/customport.html#%28def._%28%28quote._~23~25kernel%29._make-output-port%29%29),
right? I'm trying to think about what the evt arg to make-output-port
should be. It needs to be the AND of the sync-readiness of all the
constituent ports, right? Is there a way to specify that? choice-evt
(http://docs.racket-lang.org/reference/sync.html#%28def._%28%28quote._~23~25kernel%29._choice-evt%29%29)
is an OR, if I'm reading the docs right..

Thanks,
Kartik
http://akkartik.name