Andrew- As SolarLynx suggested above if you want to add another AV to Comodo don't use CIS, but CF instead. You will still get an on-access Cloud AV with Comodo Firewall; the one thing that you wouldn't get is the installation of Comodo AV on your system (CF = CIS - CAV).
I would also seriously rethink your choice of AV's. Although I am not a fan of any antivirus, some are more useless than others, Baidu being in the former category. if you want to add an AV, look to Qihoo. It works well with CF and will give you whatever you are seeking in AV use.
M