Man I thought the IHS was epoxied on by some type of thermal compound. I didn't realize it was epoxied on around the die.
Anyway the hole is no big deal. Just stuff it with silicone and you should be able to fit a small O-Ring around the top of the IHS. I think it still would be better to just remove the IHS all together though and use a standard block...... I will ponder this more asi am half tempted to buy a cheap Intel system to mess with...