Would you simply have the 5 string in A# standard, or tune the 2nd string down a whole step so it's A# C# G# C# F#? Use the low string? Ignore it?
It's not metal, it's groovy rock, so it's not like the bass follows the guitar all the time, but there are some riffs where the bass follows the guitar line exactly, and would be tricky to have to pedal off the 3rd fret of the low A#. Kinda needs that open C#... but if I were actually a bassist, I might not find that a problem.
However... I'm not a bassist. This is only for demo purposes, but I'd still like to keep some sort of uniformity for whoever ends up being our bassist.
This could ultimately be a huge waste of time anyway, since the person who joins may not even own a 5 string
Why not tune it C# G# C# F# B?