I hate when customers act like that. Since you are out at work, why not just go by the male name you are going to go by? that is what I did, and I made it clear to co-workers don't' refer to me as my previous name, it took some time but they are used to it now, and when I had an old friend ask for me by my old name, it took them a bit to realize they were asking about me.
As far as customers that knew you, well they'll just have to get used to it. The ones that knew me, just look over.. lean up to another worker... is that... umm. and they just say, that's Jules, and usually customers just respond with, ah, ok to each their own.
You should tell your co-worker not to spread your business to the customers, and if it keeps happening go to your manager, what I did with a specific co-worker.