| Did you try pairing it with something other than "Mouse" as the device? There's an "other device" option, isn't there? Perhaps that will let you specify the passkey. You might even get it to pair as a keyboard, my iMac thinks my Logitech mouse is a keyboard.
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17" iMac Core Duo 1.8Ghz 1Gb | 13" MacBook 1Gb | iPod Nano 4Gb | NSLU2 Backup/iTunes Server | Soundbridge M500 |