Is it every time you paste something, or every time you leave the program and focus on another to copy something? If the latter, and you're using X, it should

Is it every time you paste something, or every time you leave the program and focus on another to copy something? If the latter, and you're using X, it should be possible to write a program that takes the selection buffer and provides a different response to each SelectionRequest in turn, letting you walk through a script pasting a command at a time without having to leave the current window. I don't know whether such a thing already exists.