Don't mess up your existing nut. You may want to switch back someday. Just get a new one. If you're willing to get some files you can make your own, otherwise any competent luthier can do the filing for you.
On my Ibe SR506 {well that was what she was when I bought 'er ; } and my Carvin LB75 fretless I switch between fourths tunings starting at F#0/E0 (below low B) , and standard low E to high F - all with the graphlon nut that's on each. That's from .185 to half that in my lowest pitched slot. Tuning is rock solid - stays right where it should even when I'm beating the bass around like a PI in a Raymond Chandler novel.
I suppose what I'm saying is if the slots are wide but filed well-shaped, you'll have no problem accomodating a huge range of gauges. I think this works as long as the strings after the nut are still straight toward the tuning peg - if there is a sideways angle leadng to the tuner it may not be as trouble free as it has been with my basses.
BEAD nut 
