SIP-T21P_E2 refusing calls issue

[Alvaro]

The issue here is that the agentes makes a lot of outgoing calls while they are logged in the system
Due to their operative the can't pause while they are making outgoing calls, in that case while the phone is on hook (could be with the tone or dialling a number) the state reporte to asterisk is "Not in use" so an incoming call actually hits the phone when the agente is dialling an outgoing call

Is there a way to send to asterisk that the phone state is off hook so that the calls in the queue are not delivered to that agent ?