reactive-programming - Vert.x - RxJava - zip without returning a new observable

Question

I am looking for a method in RxJava that behaves like the zip method, but without returning any new observable.

I have two observables, one emitting RxMessage objects and the other one RxHttpClientResponse objects. I want some kind of method that receives both objects and executes a function. That's all, without returning a new observable that emits new elements.

Any suggestion?

Thanks in advance