I do it all the time. Your relationship with the agent has something to do with setting it up. Seriously, as mentioned about most of the HGs are already illegal so they are not concerned about the 3P issue. Besides, who is going to know if there are two girls in your hotel room anyway.
When I do it, I normally do outcall, instead of going to the girls room (but usually get a room in the same hotel where the girls are staying so they don't have to walk down the street). The agent often makes you pay double the advertised rate for outcall and some of them make you pay yet again for 3P. O.o
If you are just after two girls to massage you and take turns fucking you one after another is easy.
The real tough part is to find WGs that are local and really bisexual. Meaning that they will play with each other in addition to playing with you. Once you've had enough straight 3Ps, this becomes the allure.
Girls faking interest in other girls seems even more obvious than when a WG fakes moaning. There is no passion, it's mechanical and they tend to have a 'get it over with attitude'.
The times I've had 3Ps with girls that were really bisexual it was a truly a sight to be seen.. alas that has only happened to me a few times. You can't plan it no matter how hard you try.. even if the girls are bisexual there is still chemistry required, but the more often you try the higher your chances of getting one of those magical nights.
Once you start talking about Western or European women, it's a lot easier to set up and have a good time. Most of them are at least bi-curious and will have a good honest go at it. Lastly, if you go to Tokyo you should look up Manami. I've had a 3P with her before and it was one of my top 2 all time best experiences in the bedroom. ( here is the report
http://forum.sex141.com/eforum/viewthread.php?tid=20794 )