Yeah ^
I thought vocalists picked a key they were comfortable with (seemingly out of their arses) and then you transpose songs to that one key?
And is it really that much of a pain in the arse to tune inbetween songs? Do the songs in your setlist require different tunings for each and every song? Maybe have a look at how the setlist is constructed, because I'll admit, tuning on stage looks unprofessional (well, more so than a guitar change), but again, multiple guitar changes can look a little pretentious if you're not U2 or a band of equal stature.
Or if you don't like using 5 strings, tune a 4 string BEAD and learn the songs using that tuning a find a way to do without the G?
Or, if you're not a rock band, you could get away with just using the higher octave Eb, D, C?
Truckstop