I have. I asked Mateo, who is a great sexy guy that I've been seeing for a few years now every time I visit, if he could find a guy for both me and him to fuck together (we both prefer to top). Mateo knows my type extremely well and also all of the boys so he suggested David actually. And it was great!
Yes, the rate was 50 euro per guy for 30 minutes. Since I ended spending an hour I each gave them 100 euro, so 20p euro total for a very hot hour! It was well deserved! I did also rent a private room for it because that's much more comfortable.
So the best way for a successful threeway is to build rapport and a relationship with one guy and ask him to look for a third. Because some guys don't like doing threesomes, or have limitations when working with other guys that they don't have when they are alone with a client.