First of all, the other person would not get the physical cards (I would get the second card with their name, but destroy them upon receipt), so the balances should be safe.
However, I'm unsure if the above does not open some kind of security / fraud backdoor that I am not aware of.
The purpose of the above, is to "bump" the credit score of the other person. I'm just afraid, it might also lower my score (as theirs is ~600) ?
Considering it took me quite a few years to get to the 750 (Equifax) / 730 (FICO), I want to hear all risks associated with putting someone else's SSN on my credit cards.