Thank you for contacting .
Regarding your query .
Could you make it more clearer ?
1)You want other users to use WAN when the data is not being sent to the server and when data to server starts stop other users ? Right or not ?
2)You want to disallow all the users for all the time and only allow data to server functionality for all the time? No user should use internet ? Right or Not
Please correct me .
IF you want to allow only one user you can and disallow all others , you can simply create a new forward rule .
Where you will create two rules :
1) To disallow all others
2)To allow only 1 IP address or mac address of the device that is sending data .
I hope it helps.