The M&W performance improvement package was furnished with a metering stem that DID have larger holes.
What you want to do is find a drill bit that just does fit into the bottom holes of the metering stem, and then use a drill that is one size larger. If that isn't enough you can go one or two sizes larger.
If you go to big, you should be able to compensate for it by screwing the high speed idle back in a little. If all else fails, those metering stems are easy enough to come by.