Adding events to a subscribed calendar in iCal?

[Huze]

I subscribe to a calendar using iCal. This is a public calendar at work and I'd like to add events to the calendar. Unfortunately, it looks like iCal doesn't support that behavior. Is there another way to write to a shared calendar?

For what it's worth, Thunderbird (with the Lightning add-on) *does* support the desired behavior. I'd prefer not to use Thunderbird, but it demonstrates that this is doable.