Adding Inlays

Hi, I recently bought a Sandberg bass which I love, I am really happy with this bass except for one thing: it doesn't have inlays in the fretboard (only little dots at the top), at first I thought I could manage but when I am playing from the 12th fret up I get really lost. I just wanted to ask if somebody has ever put inlays on an already fretted bass, or I am open to any idea you may have for solving this problem.

I appreciate any input you may have.