to add a function to the BGL

Let's say I've written a function to prune edges of a graph (data structures and methods are those of the BGL), in the typical C-way (declare the function header in a .h file, and write the code in the .c file). Ok, it works, but I'm not fully satisfied. I would like to make it more BGL-like. So I use templates for generic graphs, include concept check lines in my code, and I have to forget about the .h and .c style, as templates behave a little like macros, and you cannot split the declaration and definition in two files. But, is there a better way to do this, like when you add you own internal property to the graph with BOOST_INSTALL_PROPERTY? Regards, Ramón.