As I recall this is what I did a few years ago: Drive to the back of the park and park at Hotel Breakers. (The road goes to the left of the Blue Streak and wraps around Cedar Point.) Go to the check-in deck and you will "check-in". They will give you the tickets, but if your room is not ready you will not be able to go to your room and you will have to return to the check-in deck later when they will give you the room key.
Edit - I am also thinking this can be done at the front gate, but you will have to go into the guest relations building at the far right of the front gate. ... This may have moved since I have heard they redid the front gate with Gatekeeper being built. (I haven't been to the point yet this year, so I am not certain.)
Edited: 12:50 pm, July 24, 2013