If it's an outcall and they are coming to you. And you are the one in the hotel that requires an elevator key, just meet them downstairs, or in the parking lot, or in the hotel bar, etc.
When the ladies do incall, many of them try to book a place that does not require an elevator key. As more and more hotels require them, it is getting tougher to do, but if they have a room that requires an elevator key they will tell you what to do.
Sometimes they will tell you to meet them in the lobby. This is not always discrete so sometimes there is another meeting spot option. Some key type elevators may block the room floors but may allow you to go to the second or third floor, to a mezzanine, or a pool deck, something like that and the provider may tell you to meet her there instead of the lobby. Sometimes the parking elevator may have a floor other than the lobby where you can get out and switch to the room elevators. She may meet you on that floor. I have also heard of ladies hiding a key in a potted plant or piece of furniture, and telling you to grab that key. I have never run into that one myself, but have done all the others.
I have met many providers at incalls that require elevator keys. The most common thing I have done, is just walk right into the elevator with another guest or group of guests, usually fumbling in my wallet like I am trying to get my key out, and someone will always use their key first, and ask "what floor?"