iCal and Invitations

I’ve used Gmail/Calendar, and have just migrated my data back to iCal, since now I have a laptop it makes a bit more sense to have the data stored locally. There is one thing I’d like to see possible in both systems is to mark a meeting attendee as attending. It only appears to be possible to do this from the person themselves. Sometimes I speak to an attendee of a function, and they are coming, but the email or calendar system they are using does not integrate well with iCal/gCal, so the email is sent back, and I need to modify stuff manually. Google Calendar at least allows you to add “Guests”, something I haven’t yet figured out how to do with iCal. However, with iCal, it appears to be possible to script iCal, so I may be able to add this functionality.