When you start a franchise make sure that edit rookies is on.

Then when you reach the off-season, and get to the draft, when it's your pick, come out of the draft, go to front office, then to rookie scouting.

Once there, go to the position player that you want to draft, highlight the player, then press the X button.

A menu will appear and ask if you want to edit player? Press the X button and voila!!

You can now make super rookies to add to your team.

P.S: Don't worry about signing them to big contracts because you will be able to sign them for little to no money based on their draft position.