[quote name='waynepunkdude' post='1148183' date='Mar 3 2011, 11:16 AM']You could get a DI box and tell them the sound man is sorting them out tonight.[/quote]
Plus one. Just tell them to DI.
When I, for some reason, cannot get a full rig to a gig, or their is no time/space, then I just take the Tonehammer or Sansamp. Yes, you wont have that 'rig sound' behind you, and your guitarist(s) might be wary of it, (I know mine are) but it works and does 80% of the job, the other 20% is relying on the monitors to hear yourself so that depends on the soundman. If you dont DI though, and you tell them they have to, then its not your problem.
DI-ing bass with a decent pedal/DI box has come on leaps and bounds, so its not like they are going to sound really poor.