Hide Forbidden Combination


please let me know if i can hide the value of a forbidden combination in options.

For example here http://www.katoikianet.gr/index.php?dispatch=products.view&product_id=33106 i would like to hide the second option “Χρώμα” when i have select in the first option “Πορσελάνη”.

I want this option too. Anyone have any ideas how to implement this? I want them actually hidden, not just greyed out and unselectable.