question

Use the Escort Patient > Process activity type to escort the patient to the destination, like it sounds like you are doing but set the process time to zero. Then start a new Process activity with the staff destination set to the Check-in Desk object.

Put your process time there, and the staff will leave the patient for the duration of the process time you enter.

EDIT****

I misread your question a little initially, the above applies in general principle but more specifically fr the appearance of being behind the Check in location, you may need two process activities with different staff destinations. So do a process activity with a time of Zero, and tell the staff to go to location that is behind the desk, this could be the staff's group object or a placeholder object that just serves as a destination. Then give another Process activity for the check in desk with the proper process time. The two-step process here is to make sure that if the staff turns their back to the patient to walk behind the desk, they will reorient when you tell them to go to the desk.

twostepcheckin.fsm