Originally Posted by
deltagoldflyer
Call MR (not the AMEX CC line) at 1-800-297-1300
Ask them to "de-link" your other cards from your main MR account and setup new ones for each card.
BINGO you are all set

^
BTW you will need to have a new login for each card now at AMEX but well worth it for the points you could get and end up with long run.
I think you can do it under just ONE online username. There will be two different MR acct listed on the right hand side.