I also searched the forums for the same thing you're asking about, but couldn't find anything. Here's the solution I came up with...I doubt it's the best way to do this, but if you only need a few speeds (like sneak, walk, and run), this should work.
(edit) the last command was when I started on the move left commands, it's not finished. The first three blocks are for right analog movement.
hehe thanks, I was thinking in do something like that