how to organize bookmarks (bookmark.el)

Hello I am using Karl's Fogels bookmark.el Since I meanwhile have a lot of bookmarks I would like to organize them in a way. I came up with un ugly hack using outline-minor-mode. But what I am missing most is the possibility to have various bookmark files and not just one global one. For this it seem to be bookmark-set and bookmark-bmenu-list should be rewritten in order to allow a different .bmk file as an argument. Has anybody an idea how to do this. Karl said he would not generalise the package. Regards Uwe Brauer