rc.d: how to daemonize a non-daemonizing daemon?

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

I'm trying to write a sensible rc.d script for cups-browsed. Unfortunately, 
cups-browsed itself does not daemonize. Now, that's not hard in shell:
	( cd /; cups-browsed "$@" <&- >&- 2>&- & echo "$!" >$pidfile ) &
but how do I incorporate that into an rc.d script? There seems to be no way 
to set command to a shell function executing that code. If I set my own 
start_cmd, I loose all the magic foo rc.subr does for me. do I need to put 
that piece of code into a shell wrapper file or is there a simpler and 
more elegant way?