Simple
1. By a new hitch with the legs that are integrated on the hitch frame made for the trucks puck system.
2. By a picture frame adapter that also fits the pucks that should accommodate your existing hitch.
3. By a hitch that will use the gooseneck ball such as an Anderson ultimate or B&W companion.
Option 2 is the most economical and logical choice if your happy with your current hitch. If not then sell it and go with 1 or 3. The B&W companion is a hoss of a hitch that you will be very hard pressed to find any negatives on
Really these are your only logical choices. Absolutely no way I'd put rails in a brand new truck that has the fifth wheel/gooseneck prep package. I'm not even sure you can.