So you may or may not be aware that adding “?sl=1” to the end of the meeting URL in a Lync Meeting invite will force the client to use the web app. This can be nice if you’re chatting with firms that you’re concerned may not have federation set up properly, or if you just want to confirm a consistent experience. You can find the details on how to configure that up at the end of this Microsoft article: http://office.microsoft.com/en-us/join-a-lync-meeting-from-lync-web-app-HA102828539.aspx
Now, what if you want to set this as the Lync meeting invite default? How do you customize it? Well, you can’t. This is where this terrible hack comes in. If you’re like the majority of deployments, you’re configured to use the same dedicated meeting space each time. This means that your Conference ID and web link don’t change. What I suggest, and seems to work reasonably well, is to modify the invite to look the way you want, get the phone numbers in the right order, add that ?sl=1 link, give a little extra information. Then, cut and paste the meeting into a new Outlook signature called “Lync Web Only Meeting” or whatever works for you. Now if you want to create a custom Lync meeting invite, just create a regular new meeting and insert your signature.