No, currently there is no viewer plugin capability. It's on my TODO list, however I havent got to it yet as its fairly painful, the viewer has independent processes that co-operate (it's essentially a browser) and different processes use different languages for their code, (rapydscript and python). So creating a plugin framework for it is not easy.
That said if you wish to help with such an endeavour, I can be persuaded to move it up my TODO list
