There is a Castilian Spanish version, which comes together with the German version (you can get it either through www.fnac.es
). Region 2, and all that.
I own the season 3 set with the Castilian Spanish dubbing (it also includes German dubbing). In that particular episode, when you listen to it in Spanish, Leela simply says her line in perfect Castilian Spanish (the original has her saying her lines with an exaggerated American accent) and the director of the ad speaks with a Mexican accent. That's all
I guess it was a bit of a cop-out, but well... C'est la vie!
(In an unrelated subject, the Castilian Spanish dubbing of both "Futurama" and "The Simpsons" is awesomely good. I know for sure that in 2000 they won an international prize for best dubbing).