Can't be done, sorry. It appears as if it's part of RIM's internal API, as the Yahoo! Messenger and Google Talk clients they programmed for those respective companies add service books, but there's nothing in the API for adding our own (yet).
Send them an email and ask for it. I think it should be part of the API, as it's just opening up a proxy but they might not if the carriers can't control (and measure) data flow.
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