Yes there is a way to do this, but no it is not a basic feature.
You would have figure out how to and implement the changes to get this to work yourself at the PHP level. If you are not familiar with PHP then you cannot do this. You would have to change how the drop down is populated by changing the query to only pull people who are in the same group as the logged in individual.
In general you would edit /include/staff/newticket.inc.php circa line 168 onward. You would need to get group_id for the current user. Then modify the sql= line and add to the WHERE section of the query "AND group_id=$current_group_id ".
Beyond that you are on your own in implementing this. Good luck.
