The only way around it is to say some job that one cares about like working at Timmie's/Walmart or even as a secretary in some boring office job. temp services, call center work, which you have done. Or say that your are in school, studying something you actually know a bit about or telling the truth about what you do.
The only issue with that is that it makes for a very bad foundation to a relationship. When I first got out of school I was underemployed, and since I have no dependants if I leave a job I often slate a couple weeks off between jobs, and I've walked off a job with nothing new lined up.
In all of those cases I've had the awkward conversation... It can only be worse for sexworkers, but you can't fault people for asking. It is a legitimate job hazard of all sexwork. All you can do is say what you do and let the chips fall where they may. By all means invoke "client SP privilege" if you want to move the conversation along, BUT:
-How long is such a big lie sustainable?
-What does it do to your conscience?
-What happens when you tell him?
-What happens if you get caught?
-How much worrying do you have to do about getting caught?
Your work is a big part of your life, maintaining that sort of lie would be more trouble than it's worth.
Hey, I'll not fess up to my SC crawl fetish, but that's black-holing one night a month**. (Mind you I'll fess up to having been at SCs and about guys nights, etc.) But there's a big gap between maintaining that fiction, and it's weight on my conscience, and me walking around saying, "I'm TOM and I'm an eye surgeon."
** I'll generally skip my crawls for a while if I go into a mono thing, or something that has that prospect. When I do eventually lurch back to crawling I'm the lowest mileage customer in the GTA today. But that's about me.