I've made a userscript that offers me a way to bind a key combination to a clickable element chosen by a xpath expression. It still misses a way to easy edit previous bindings but I'll provide it later, I promise!
You can still edit the bindings (well, more likely remove them) via about:config (the 'greasemonkey.scriptvals.ShortcutBinder/Shortcut Binder.bindings' setting).
Grab the script from here.
For a quick overview (bunch of screenshots) check this: http://code.google.com/p/webmonkey-userscripts/wiki/ShortcutBinder
Ah heck, here's one quick and dirty: