Sounds like this is the wrong way around. Why should the airline take on the task of adding names to a wait list, with first come gets offered first, or they don't know you got another seat on another airline but did not tell them, or you change your mind and did not tell them, or they offer a seat and you turn it down for any other reason. How long are they going to wait for you to read your emails and take up the offer before offering it to the next on the list? How is all this going to work? Who is going to do this?
If you want a seat it is up to you to keep looking.
If a seat comes up the first to book it gets it.