I looked at the source code for jQuery Ajax, and saw that it is basically a wrapper for the xmlhttprequest object. So I made my own wrapper, one where I don't have to specify the same parameters every time.
But the solution we use is something completely different which is hard to explain in a single post. It is based on CQRS and provides not only a way to communicate with the server, but validation of parameters. This works very well with Knockout observables, since you can create an object once and then execute it multiple times, when the observables have changed.