runlevels and init scripts

This may be a silly question, but here goes.

I use different runlevels on my Gentoo laptop for different power
management states.  So far, so good: when I switch states, everything
starts and stops the way one might expect.

But there is *one* service I start manually that I want to *ignore*
when I switch runlevels.  If it's started, I want to leave it started
and leave it stopped if it's stopped.

It shouldn't be tough to make the init script to do this, but it's
almost always the case that when I think up a "new" feature, someone
smarter has already done me one better.  :-)

Is there a standard way to *conditionally* run an init script?

TIA,

Dylan