[boost] metrics and tree stuctures

I'm interested in adding support for arbitrary metrics (euclidean distance, taxi-cab, etc) to boost so that I can make use it, as well as some alternate tree structures, such as kd-trees. I can't quite figure out where they would be most appropriately placed, and it doesn't seem as if there is enough (or enough similarity) to have a totally separate library. Anyone have any thoughts? Kevin