Ah, yes. I remember from your prior post that you have very large databases and table sizes and are considering (or have begun) partitioning the largest tables. It turns out there is an innate partitioning scheme built into the most recent MySQL versions, but it has to be compiled into the running binary by way of a compiler flag:

http://dev.mysql.com/doc/refman/5.1/en/partitioning.html

I apologize if you've already heard this, or if it's already in place as a partial solution.