I would politely voice my concerns to the BL. As I've stated in other threads, back when I played cover bands, I was always upfront, I won't play Mustang Sally, ever. They have always obliged. Permanent and sideman. Ironically, the good cover bands I seen, and believe me, those are super rare, don't play those standard cover tunes that everyone on here claims is a must play. But that is irrelevant tothe conversation. I say speak up, talk to them or the BL and let them know how much it's bothering you.
Where Lead Singers and guitarists often seem to have a reputation, and usually live up to it, of having big ego's, it seems many bass players are very submissive almost in just terrified of speaking up as if they are not in the band. Granted, you are not in the band, but You have a voice, use it. Squeaky wheel gets the grease. I doubt they are willing to fire you over your desire to veto one song.