How to setup Auto-Answer for calls going through queue (ACD)

Hi there,
I want to setup “Auto-Answer=yes” for my phones when they receive a call from the queue. I have tested the Auto-Answer function of the phones (Snom320) by adding a SIP-Header and dialling the SIP extension - this works perfectly: The dialplan snippet is shown below:

exten => s-test,1,Answer
exten => s-test,2,Wait(1)
exten => s-test,n,SIPAddHeader(“Alert-Info:;info=alert-autoanswer;delay=0”)
;exten => s-test,n,Queue(my_test_queue|tT|||600)
exten => s-test,n,Dial(SIP/1234,120,tr)
exten => s-test,n,Hangup

If however I send the call into the queue (commented out in the snippet above), the phone keeps on ringing until an agent manually answers the phone. Problem seems to be that the queue does not make use of the SIP channel - but how can I then add a SIP Header to the calls coming from the queue or is there another way to enable auto-answer for calls coming from the queue ? Any help or ideas will be hugely appreciated.