Hidden Players: At the Create Player screen, enter the following names:

Raja Altenhoff
Tom Braski
Craig Broadbooks
Peter Dille
Josh Hassin
Jody Kelsey
Tawn Kramer
Craig Ostrander
Kelly Ryan
Alan Scales
Chris Whaley
Enter 1 for the player number, F for their position, 150 for their weight, R for their handedness, and leave all the other numbers the same. When you go to the Sign Free Agent screen, you'll notice that their overall abilities are 99.