It works slightly different than most .MSI/.MSP patches but it can be done.
1. Place "Communicator.msi" and "Communicator.msp" (from the latest RU download) in a directory called C:\Install\
2. Make a directory inside C:\Install\Communicator\
3. Run this with elevated rights: msiexec /a C:\Install\communicator.msi targetdir=C:\install\Communicator\
4. Run this with elevated rights: msiexec /a C:\Install\Communicator\communicator.msi /p C:\install\communicator.msp
5. Run this with elevated rights: msiexec /i c:\Install\Communicator\communicator.msi REINSTALL=ALL REINSTALLMODE=vomus UPGRADEEITHRECACHE=TRUE
6. Enjoy your newly installed and patched Office Communicators Server Client!
The communicator.msi inside the C:\install\Communicator\ is the patched and updated .MSI instance.
You will still need to use the "REINSTALL=ALL REINSTALLMODE=vomus UPGRADEEITHRECACHE=TRUE" parameters when installing that particular .MSI
Many tips and tricks about this came from this TechNet thread here.