Share 'Method for cleanly cutting back fretboard.'

I am needing to adjust the front edge of a strat's nut slot to accommodate an LSR roller nut. How do I make the cuts parallel and clean--I know where to cut, I am just really hesitant. Please offer specific methods and tool descriptions. I was thinking of a jig or mitre box arraingement, but so far I haven't found a mitre box with the precision and capacity I am looking for. Thanks! i'…