I cut a Cinelli stem to use a slanted lock nut. I used a Dremel tool with the thin cutting blades. It took several. It can be done and you just need patience. A bench grinder helps a lot. Your bolt may end up being too long. (precisely why I had to change bolts on the Cinelli)
Two questions:

1) Are you just trying to get it in to the insertion line to be safe?

2) How much farther down does it need to go to fit you?

If 1) is yes, I'd cut off about 1/2 inch.
If 2) is less than 2", cut what you need to for the fit. If it's more than 2", I'd think about it more.

It sounds like you need to cut 1/2 to 3/4 inch. Have at it. Been there, done that. Take your time, and it will be cool.