1.) Make sure you have 1 prestige token available

2.) Have a friend invite you in the Xbox Live Lobby

3.) Go to Barracks > Prestige Shop > Extra Custom Class

4.) You should be over the "No"

5.) Have your friend search for any match and then back out as soon as you are both searching

6.) Now you should still have that pop-up but NOT be able to navigate UP and DOWN

7.) Go to Barracks > Prestige Shop > Double XP and click Yes

8.) Now you should have another pop-up, make sure you click YES to that too

9.) Look at your prestige tokens - it should now be at - 1

10.) Now you may buy everything from the prestige shop that's available to you

NOTE: I do not take credit for this, I just found out how to do it without being first prestige.