Although probably intended to be playable on a keyboard, Bach's original edition was written in score form, so I don't think a string quartet version would be any easier to transcribe for clarinet quartet than the original. Mainly you would have to deal with the transposition. One transcription for string quartet by Robert Simpson and recorded by the Delme quartet transposes the entire work to better suite the ranges of the string instruments, so transposition would not without president. The original is in d minor, so presumably you'd want to transpose to the relative minor of B flat, or g-minor.