SSH in and put your AIFF in the corresponding location:
These are the default system files, and they are found in /System/Library/Audio/UISounds
alarm.caf, beep-beep.caf, dtmf-2.caf, dtmf-0.caf, dtmf-1.caf, dtmf-3.caf, dtmf-4.caf, dtmf-5.caf, dtmf-6.caf, dtmf-7.caf, dtmf-8.caf, dtmf-9.caf, dtmf-pound.caf, dtmf-star.caf, lock.caf, long_low_short_high.caf, low_power.caf, mail-sent.caf, middle_9_short_double_low.caf, New-mail.caf, photoShutter.caf, ReceivedMessage.caf, RingerChanged.caf, SentMessage.caf, short_double_high.caf, short_double_low.caf, short_low_high.caf, SIMToolkitCallDropped.caf, SIMToolkitGeneralBeep.caf, SIMToolkitNegativeACK.caf, SIMToolkitPositiveACK.caf, SIMToolkitSMS.caf, sms-received.caf, Tink.caf, Tock.caf, unlock.caf, ussd.caf, Voicemail.caf
Hope this helps.