Brown's Guitar Factory - Fretted/Less Bass...
Brown's Guitar Factory
Johnny Brown BGF Fretted/Less Bass - YouTube
After looking at the Browns page, they have a model which is Fretted/less chambered. (Sorry I can´t post the pic). This bass has frets above the 12th fret, and is fretless below.
Now, I may be missing something here, If you played the fretless part of the neck, wouldn´t the strings always hit the 12th fret?