Maybe the culinary branch of the
Turbo Careers mod would be what you're looking for? I've never used the mod though so I don't know whether or not it's working.
As for a mod-free solution, there wouldn't be too many options. You could buy a portable bar and a sales table and sell drinks at the club? You could make a restaurant that functions as a bar and only serves drinks maybe?
or to have played sims take over positions for NPCs
I don't think this one is possible
eta: but if you have GT you could also drop the bartender into a club that meets at the nightclub and mixes drinks