i've had similar dilemmas at the local clubs i frequent. i only have to really worry about this at two of those clubs, since at the other clubs, the turnover is so frequent, i haven't developed any lasting regulars there. But if these girls are your current favorites, you can still throw them a bone and do just one or two dances with them. You should still probably end up enjoying your time with them as they are your favorites for a reason. In my experience, i've rarely regretted getting A dance from one of my favorites; in other words, i'd rather get a couple dances from a sure good thing than get several mediocre dances from several unknown commodities. i mean my favorites are the actual reason i go back to a club and hope they are there. Not that i don't want to try something new or something good, preferably new and good, in which case i might have a new favorite.
But the other posters are right. Those girls probably also see you as a sure thing and you shouldn't let them get too comfortable with that. That's why i think the one or two dances that you do with them pretty clearly lets them know that you're not going to spend that much money on them and they can't really get all huffy and puffy without looking ungracious and potentially losing a source of regular income.
You can also try throwing some complements, questions, interest towards one of the new girls or other girls you might be interested in while one of your current favorites sits with you. You can say like, "Who's that girl?", or "She's hot!" when said girl is on stage or walking nearby as i tend to zone and not engage too much and start looking at other girls when i'm not too interested in the company i'm sitting with. We usually end up watching other girls anyway and strippers just are unable to resist gossiping. Then your fav might get the clue that you're interested in other girls and clearly not a onegina man.
Now if these girls are getting long in the tooth, then who really cares what they think. They already know you're a regular customer who probably spends a decent amount of money and will come around if they're in a rut and you show them some interest again.