Yes it is possible, as we have just successfully completed testing our proof of concept for Lync Online.
Two of the major hurdles that we encountered were:
- Lync 2010 required this patch http://support.microsoft.com/kb/2912208, to work with Lync Online
- Our Sidewinder firewall Deny Rules completed the three-way handshake for TCP, causing Lync to think a direct connection could be established. This was re-mediated by changing Deny to Drop.
Other things, such as needing to bypass SSL inspection, were relatively straight forward once the above two points were discovered and fixed.