Im an AU on a CC, and my credit limit is not at the max (the original user limited me to $2k. Does removing that low credit limit make it better for the $2 trick? Should I ask him to remove the limit?
I may be wrong, but the 'credit utilization' portion of your credit score will be based on the entire amount owed on the credit card and the entire credit limit. Your portion won't be separated out. So if the primary on the card would do the trick, it would help you. If he keeps high balances it would work against you.
But if this is your only card, keep it until you get one of your own.