There is a Lync (UCWA) API to do this at http://msdn.microsoft.com/en-us/library/office/dn356790(v=office.15).aspx
This API does not support impersonation, so if you want to create a Lync meeting on behalf of another user, your application will need to somehow get the user's credentials to sign in and get an OAuth token. Once you have a token, you can call the API to get a JoinUrl
.
If desired you can then place the JoinUrl
for the meeting in the body of a calendar appointment you make with the EWS API.