SIM Blocking once data allowance reached converted into 'no outbound traffic' firewall rule

We have many HD2 and HD4 boxes that only have SIMs in them no fixed line connections.
Sometimes the users on a site will use up the entirety of the data allowance and the SIM gets shut down, which is fine.
However if all the SIMs get shut down by enabling the check box; you can now only manage the box from the LAN.

Feature request:
Once the data allowance is reached rather than disabling the SIMs, is it possible to add an outbound blocking policy to stop further traffic using the SIM but crucially still allowing access to the box.

A really clever feature improvement might be to have a block all outbound or a check box to allow InControl, or a pre-defined IP, to still interact with the box (this would incur data overage charges but give full management of the equipment.

Can definitely see the advantage in this!