That is a great idea. I tried it once before I had the $$ for a 5 string. The problem is that your nut is cut to fit normal strings. You would have to replace or re-cut the nut to make the much larger strings fit. I didn't realize this until I was about to bring the strings up to pitch. OOPS!
My solution at the time? Boss Octave pedal. Used, like $50. You don't need the really low notes most of the time anyway, so I just set the octave pedal to emphasize the lower octave and when I wanted the notes I kicked on the pedal. This can make for some interesting tap dancing, but is really fun when you get into the challenge of it. Hope this helps you.