[boost] extending type_traits::rank ?

I need an equivalent of type_traits::rank for a vector-matrix library I am working on so I thought about extending type_traits::rank for my own vector- and matrix-types. But is extending type_traits foreseen or even possible? And what is the best way to go about? The easiest way of course is to add a specialization for boost::type_traits::rank in my project's sources but this is not a very clean solution because this would require that I add stuff to the boost-namespace in my own project. Ideas? Thanks in advance, toon