Please note the requirement you have there is not a supported one and cannot be achieved. UCCX by default will not deliver any ACD call to an agent till the time he/she is in Talking state. As far as increasing the Busy Trigger from CM is concerned, then that also will only work for direct (Non-ACD) calls to the agent extension only and not for ACD (calls coming through UCCX). However, increasing the Busy Trigger to a value other than 1 is also not supported. Refer Unsupported Configurations for Agent Phones of below document that states this:
http://www.cisco.com/c/en/us/td/docs/voice_ip_comm/cust_contact/contact_center/crs/express_11_0/release/docs/UCCX_BK_R7697E6E_00_release-notes-for-uccx-solution/UCCX_BK_R7697E6E_00_release-notes-for-uccx-solution_chapter_01.html
In nutshell what you want cannot be achieved and is not possible with UCCX.
Regards
Deepak