Stock curled home a free-kick from the edge of the box before Ormerod bundled in a second goal late on.
The win secures home advantage for Preston in the second leg of their semi-final on 8 May, with the first leg at Elland Road on 5 May.
Another boost for Preston was the early return of leading scorer Dave Nugent, who came on for the final few minutes - just over six weeks after breaking the fifth metatarsal bone in his right foot.
Leeds had made eight changes for this game and will have to do much better when the two sides meet again next week.
Preston dominated for long spells and saw Daniele Dichio head straight at Leeds keeper Neil Sullivan from six yards out, while Paul McKenna and Simon Whaley also went close before Stock's goal.
Robbie Blake sent a low free-kick skidding wide for Leeds before half-time but the visitors had run out of ideas even before Ormerod struck from close range to wrap up North End's win.
Preston manager Billy Davies:
"We are delighted to finish with three points here, with the clean sheet record for the season and with six defeats out of 46.
"I really can't explain how it feels to be in the play-offs again this season.
"To have that ticket again and to look below at some of the teams who have not made it makes me very, very proud."
Leeds manager Kevin Blackwell:
"I put a team out to be competitive and it was, so I'm pleased with what I got out of it.
"There were a lot of changes but it was for a purpose.
"The occasion will have to be dealt with in a separate way. Training becomes a lot more specific so I'm pleased it's out of the way."
Preston: Nash, Alexander, Davis (Wilson 45), Mawene, Hill, Whaley, McKenna (Sedgwick 67), Jarrett, Stock (Nugent 84), Dichio, Ormerod.
Subs Not Used: Agyemang, Lewis Neal.
Booked: Wilson, Alexander, Whaley.
Goals: Stock 38, Ormerod 77.
Leeds: Sullivan, Richardson, Gregan, Kilgallon, Pugh, Walton, Blake (Griffiths 66), Stone, Douglas, Healy, Moore (Beckford 51).
Subs Not Used: Bennett, Einarsson, Harding.
Ref: U Rennie (S Yorkshire).
Play-off semi-final dates:
Leeds v Preston
(Elland Road, Friday, 5 May, 1945 BST)
Crystal Palace v Watford
(Selhurst Park, Saturday, 6 May, 1215 BST)
Preston v Leeds
(Deepdale, Monday, 8 May, 1945 BST)
Watford v Crystal Palace
(Vicarage Road, Tuesday 9 May, 1945 BST)
Play-off dates for other divisions to be confirmed