I'm using this plugin by sabret00the:
http://www.vbulletin.org/forum/showthread.php?t=99498
To get it working on vBadvanced CMPS, $navbaravatar simply needs to be globalized and luckily the application comes included with a little tool that allows you to do exactly this! Go to the following location in your browser:
Admin CP -> vBa CMPS -> Default Settings
Scroll down the page slightly, and find the "Portal Output Global Variables" settings. Note that the description here states that the '$' before the variable name is NOT required, so simply enter
navbaravatar there, hit "Save" and you should be good to go.