Though I'm not very good by any measure at tapping.
I found 2 interesting ways to approach it.
one is keeping with the one finger per fret rule and tap out scales just as you would with your fretting hand doing hamerons but with your picking hand on above the 12th fret... if that makes sense.
Another one is actually learning how to play a little piano, what this does is show you how to apply the two octaves at the same time.
Well there's my good or bad advise, someone please correct me if I'm wrong.
oh and there's this wooten video
http://www.youtube.com/watch?v=SocYTUn-NQA