Here's how you do this in Outlook 2010:
Decline the meeting so the person knows you aren't attending
Go to the deleted items folder and open the invite
Click "Tentative" and then "Do not send a response"
Open the appointment and then change your time to "Free"
These are the same steps that Microsoft says in Show a declined meeting on my calendar.
These steps only work when you just received the meeting invite. It will be difficult to find the meeting invite for declining one occurrence of a weekly meeting that has been running for a while.
