One way to do it:
In a terminal do cardctl eject. In konsole it's already pre-configured in the drop-down command list.
To activate your CF wifi card again do cardctl insert
Bonus hint: If you go to a coffee shop and you're trying to get on their network but you're not getting a lease, even though you've made the proper network settings, doing cardctl eject && cardctl insert will help by resetting the card.
Hmmm, on the other hand, my Opie does have the taskbar utility to eject the card....