Dillion Power trimmer die question

I use a Dillion power trimmer for my rifle brass. I prefer to neck size the .338's. The dillion dies supplied for the trimmer are full length dies.

Questions; How far above the belt would I have to machine the die to keep the cases neck sized? If I opened the die diameter from the belt up to the shoulder by .0015 would it work the same as a neck sizing die??

Thanks!