You must have Premiere Club, unlocked Sanctuary, and have a second Controller.
1. have main account at Sanctuary
2. plug in second Controller, hit the Guide Button and Create new Profile.
3. on Your Main Controller hit start. on the second Controller hit (a) to join.
4. golden key unlock for second controller. use main Controller to pick up purple loot.
5. on the second Controller hit the Guide Button and sign out.
6. still on second Controller Create new Profile again and repeat steps 3-5
7. repeat till you are stacked with purple.
notes:
you will only get lower level items as its a new character that unlocks the keys. you could level up the account before using the key.
If a buddy doesn't have the Premiere Club, is ranked up and trusts you with their account you could do this and dupe what ever loot you get it.
if You dont know how to dupe weapons leave a comment and ill do a guide.