The obvious one is to get the vocalist to really get close to the vocal mic and like touching it. (kissing!) Then you can turn the gain down and still get a decent level out front. Really vocalists live should be doing this anyway. Then you will find that the vocal track will be loud and the other instruments will be pretty soft in the background.
Same thing too with the guitar and bass. Record the bass direct, that problem solved, and also mic the guitar cab real close too and you won't get any vocal bleed into the guitar mic either.
Are you about to do this recording or has it been done already. My advice only applies before the fact. Trying to repair this sort of thing after the fact is much harder.
The best you can do though is actually start with the vocal track and get it sounding as good as you can even with the other stuff in there and then maybe just bring a little of the other two things in. You may just get away with that. Also when putting a high pass filter on the vocal to try and reduce the bass spill use a very steep slope e.g. 48 dB/oct and bring it up to the cutoff freq that gets rid of some of the bass without changing the vocal sound too much. The guitar is a bit trickier though.