I agree with ROCRKE who commented before me. This is not a lame idea at all. She should "understand what he means" and be perfectly happy to suck his penis for more money. Absolutely. And get a free facial while she's at. It's good for her complexion and character, plus she won't get pregnant this way.
This isn't a lame idea, I did this too. I went through three different maids, before I found one that would do anything for more money. Just don't let them move in, or your asking for trouble.