hold the fifth fret on the soon to be low b string and get the tuner to register an E.. wont be as accurate but if your intonations ok then it should be ok
same for the other b string and you can go off the notes on those strings and tune off them... or just get a better tuner
__________________
Musicman bongo 6 HH|Ibanez sr506|gk1001rbII 1x15rbh
Gallien-Krueger Club Member #386
G doesn't move, tune D-string to B using A-string (2nd fret) as reference, tune E-string to B using the other B as reference, tune A-string to F# and you're done.