It's a secret (oops!) long-held ambition of mine to play these on bass one day, but setting up an instrument in 5ths specially seems a bit like cheating to me 😄
I guess one could play around with the D’Addario string tension calculator (there seem to be various string tension calculators online but as far as I can tell they all acknowledge D’Addario’s data), or just try some out. If you started from a standard 5-string set you could do BFCG using the B and G strings at pitch and the E and D strings respectively tuned up and down a tone, or from a 6-string set EBFC in a similar sort of way.
I do possess a 5-string fretless that I haven't settled on a stringing for yet, and a variety of secondhand strings, so I could have a go at some point and report back. I haven't properly started trying to learn fretless yet though, so I won't be sharing any attempts at playing Bach on it for a while…