I don't know anything about this subject, but my first thought (which may be wrong) would be to just set the weight of the new server to be the same as one of the other servers that are receiving messages (perhaps one of the lower ranks). In that way, it would not be overloaded so easily and adjust its ranking after a while
I guess my explanation was lacking then, as that wouldn't help. reducing the weight below the old nodes might work, but it would also extend the duration you're overloaded, which would also cause requests to fail.
