Edit the ADE and add some parking to the Signature ramp and then GSX will give you some options at those spots.
I think what would be excellent to have added to GSX is the ability to customize or label the aprons. So instead of for instance just having Parking spots 52-73 and having to guess where they are on the field, you could label them as being at Signature etc. It would make requesting parking much more intuitive within GSX.