What you said
Find something that the child will want to avoid. Enlisting the assistance of parents in advance can help. Go over to the child and whisper in his ear: "Joe, you're on your second warning. If I have to send you out, then I am calling home - and if that happens, apparently you can forget football this weekend. Give that some thought." Then walk off and let him decide what he is going to do.
My school has a three-strike policy in which students are sent to the "safe room" with work to do and automatically get a half-hour or hour-long detention. We always have two rooms allocated. If another student is trying to be sent out, I point out that they will not be in the same room as their friend and that I am prepared to ring home about their attitude if it continues. This usually does the trick. Also, having lots of work prepared for them to do (even if it is just from the textbook; it doesn't need to be interesting) means that they actually learn while they are excluded.
The expert view
Sending someone into a corridor is not a sanction - it is an opportunity for them to cool down for a few minutes or think about the way they are behaving. I do not find it particularly useful for most occasions. If someone mucks about to the extent that I need to have a chat with them during a lesson, I usually just give them a detention - then you can have all the chats you need. As you say, being sent out is used as a tactic by some children. Good luck.
Tom Bennett's latest book, Teacher, is out now, published by Continuum.