I really hope a hook exists or is added then since this could be quite a nice way to use up spare ruby and sapphire blocks (emerald blocks can already be used per vanilla).
Big fan of your work by the way, please keep it up
Well, if there isn't a hook, there might be in future versions of Forge as I decided to make a hook suggestion for the Beacon Block accepting modded gem blocks as valid over on the Minecraft Forge forums. I actually linked Greg's reply in the post as a source of sorts (so they know I'm not just pulling this one out of my ass).
If you (maxxori) and/or Greg would like to keep an eye on the thread I created for updates, here's the link: http://www.minecraftforge.net/…dex.php/topic,3424.0.html