I wouldn't lose any sleep over that. I have stayed there 6 or 7 times over the years. That has been their "official" policy all along, but they don't really enforce it. I too like to take more than one guest per day into my room, and did it all the time when I stayed there. Only once did they try to tack on joiner fee at checkout. I politely asked them to remove it and pointed out that I was a repeat customer. They removed the charges quickly with no questions asked.
During the daytime, just march with your guest to the elevators like you own the place and nobody will say will a word about IDs or signing in guests. At night time they usually have a guard at a table in the lobby collecting IDs of guests and there won't be any getting around him, but that doesn't matter because as said above their guest policy fee BS isn't really enforced.
Interesting that you mentioned Landmark as an alternative, because they also have an official 1K baht guest fee policy that they don't bother to collect. This is from my email to them a few years ago in the hotel guest policy thread. Scroll down to post #25 in thread link below to see what they said when asked.....