Invest in a mill....
Seriously, I know it's £400 odd, but pillar drills aren't designed for sideways movements, the tolerances are not as close, and you still have the problem of locking the depth off. You won't have any fine feed either which would make the locks totally rubbish.
Diddn't you get a lock from me a while ago? I remember your username..... how is it holding out? Hope it taught you a lot

A little vid of me on my mill
http://www.youtube.com/watch?v=u9RmEA-Iy5Y