Wouldn't it be better to see if you can find some other sort of release than cutting? (yes, I know what you said...)but so far I have never heard of cutting helping anyone in the long run).
as for scars DONT cut.. However, if you will cut no matter what, make sure to make the cuts small and "clean" As soon as you start going deeper or make hurried, jagged cuts, you will have scars no matter how you do it... and it seems to me that most people who have been cutters for some time start to go deeper.
Isn't there some natural release (i.e. hard exercise) that could take your mind off the urge?