There is no support for this. Kamailio in its proxy role (the role you are invoking) is pretty much event-driven, in the sense that it's processing is real-time and correlated to the receipt of messages to be forwarded. It is externally stimulated into action.
Also, it would be quite problematic from the perspective of SIP protocol mechanics. If you do not even send 100 Trying, the sending UAC will retransmit the INVITE, and/or eventually assume your proxy is down. If you do send 100 Trying but do not follow up, other timers awaiting final positive or negative replies kick in and also expire.