Two simultaneous calls on Agent

I have a queue with several agents login on it. The strategy of tail "ringall."
These agents login on sip extensions that are configured in SIP SPA942 phones with the ability to “call waiting”.
When all agents are busy, if another call comes in the queue, this was put on hold.
Is there any way to make the call go to the agents, although they are in Busy?.
This is possible if the tail sip extensions are putting the parameter “ringinuse = yes”. But agents in the queue, to detect the “busy”, the call does not come automatically.
This can be solved somehow?

The version I have of Asterisk is: Asterisk FreePBX