They're not THAT expensive...

If you have a relationship with a local machine shop, you might ask what it'd cost to ream the die for you, rather than doing an uneven job by hand yourself.

Even hardened, you can always drill, grind, or lap out the neck of a die, only difference is the equip you have to use and the time it takes to do it.

If you screw it up, you're out the cost of the die. Might be cheaper to modify an FL die and easier to find, so if you're OK with maybe botching the job and needing to replace your FL die, go ahead.

Are you wanting just a body die, meaning no touch on the shoulder, or just to take off the contact from the neck?