Well, you could run a simple batch file, which would be in some easy to access place (your desktop or quick launch). If you named it b.bat you could call it with just a "b" keystroke. Best would be to have it copy your bookmarks.html to your second hard drive, if you have one.
Likewise I suppose you could have a single batch file close K-Meleon and ALSO save a backup batch file. When you executed that batch file, it would certainly seem as though you were creating an automatic backup.