Opening Lync Metro conversation from a Windows Store App

Hi,

I'm trying to open a Lync (metro app) conversation directly from my Windows Store App. 

I can achive this in the Lync desktop version by using the following command:

Windows.System.Launcher.LaunchUriAsync(new Uri("sip:someone@domain.com"));

But I can't achieve the same result with Lync Metro. The only protocols I've found were lync15, lync15mlx and tel.

I tried to pass some parameters with lync15 protocol, like "lync15:sip:someone@domain.com", but it seems that the protocol ignores every parameter so far.

With the protocol "tel" I can make a lync metro call (tel:12345), but the instant message chat is disabled for some reason (even running with full permissions).

Is there any protocol available for the Lync metro app to start a conversation? Are there any other protocols besides the ones I listed previously?

Thanks.