NO CREDIT GOES TO ME FOR THIS. I DID NOT DISCOVER THIS. I FOUND IT.
Use at your own risk. Bioware may or may not ban you from server. Also get you ban from Xbox live.
1: START A GAME WITH 2,3 OR 4 PLAYER ON BRONZE, SILVER OR GOLD. WHATEVER YOU ARE GOOD AT.
2: GET TO WAVE 10 (OBJECTIVE MISSION)
3: ONCE OBJECTIVE IS COMPLETE. ALL PLAYERS MUST DIE. WAVE SHOULD NOT BE COMPLETED.
4: ONCE EVERYONE IS BACK IN THE LOBBY. NO ONE SHOULD MAKE ANY CHANGES. LEAVE GAME SETTING AND LEVELS AS IS AND START GAME.
5: ONCE MAP LOAD UP. HOST LEAVE BEFORE WAVE BEGINS. GAME STARTED WITH NEW HOST ON WAVE 10 (OBJECTIVE WAVE)
6: INVITE PLAYER THAT LEAVE BACK IN GAME AND START FROM STEP #3.
7: RE DO RE DO RE DO RE DO.
PS....U CAN START ON BRONZE AND THEN WHEN U IN THE LOBBY YOU CAN FROM BRONZE TO GOLD. BUT DO NOT MAKE ANY OTHER CHANGES BECAUSE IT MAY NOT MAKE THE GLITCH TO WORK.