I know this glitch is a little old but it still works, So please leave a rating also when you join a lobby with your friend the time needs to be running down.
Written Tutorial Below:
1. Join a friend in player match and get them to search groundwar.
2. Backout by yourself and go local, hover over system link and press Y and join back your friends game.
3. If done correctly you will still be in system link. Click system link then click create a class, here you should see your online classes.
4. Go to perks and press X to toggle pro perks, on the perk that you want press X a few times and you should get a option to Buy and Equip, Make sure you do this.
5. Backout and go to player match and the perks you bought pro should be there