my sources tell me

alt+¨ (the upper one left next to the enter key)

try pressing all the keys at once (it has to be all at exactly the same time though)

For anyone still suffering from this problem, I found a fix:

For macbook pros, make sure any cds are already removed from the optical drive, then hold down CMD+EJECT+qvctyenniyp, then tap F8 repeatedly until you hear a beep. After this, pressing Enter should produce tildes. To reset, hold down the same combination of keys, but backwards.

Hope this helps someone