Delay in sending IM messages

I have some UCMA 3.0 code that send IM to a group of Lync users. It seems that there is about 15 seconds delay between when imCall.BeginEstablish() is called and when the UCMA app is actually able to send IM using imCall.Flow.BeginSendInstantMessage(). During that 15 seconds time period, the Lync recipient sees a popup that says "xyz is inviting you to a conversation". If user clicks on the popup, the UCMA app will send the IM right away. But if user takes no action, the UCMA app will eventually send the IM after roughly 15 seconds timeout.

Is there any way to send IM without waiting for user confirmation or the timeout? I need to send IM to a large group of users (e.g. alerts). 15 seconds/user would take too long.