It might be a bit
controversial, and in some parts of the
country might even get you fined for
contempt, but if you're
male you could do it the way the
Romans did it, before
anybody used
Bibles:
With your left hand, hold your testicles and swear on them.
Seriously, that's why it's called testimony.
I am told (not overly politely) that according to about.com's Latin etymology section, this is a legend. Duly noted, but pending further investigation I will take the word of my Latin teachers.