you are not giving anything thats yours rather allowing him to take from a third party, now if you would be responsible when he goes to a third party (like any regular cc charge) it would be considered you gave medin eved knani
AFAIK, from having consulted rabbonim regarding lending a CC to someone and making them (the borrower) liable for the finance charges. They all said that anything he borrows he is borrowing from ME not the CC and when he pays interest he is paying ME not the CC, even if he pays the CC directly without my intervention. Same applied here, when I charge my CC anywhere, automatically it's as if money just came out of my pocket because I just became liable to put up that cash to have to repay the CC.
but sbs is debatable since they are guaranteeing the credit (and you would not use it if not)
For the fifth time: Who the heck cares if I benefited out of giving maaser. If chayim yankel promises me 1 million dollars for giving my $1000 masser to his shul my $1000 didn't count as maaser??
Additionally, I would use my CC for maaser even without SBS, and even during SBS the charges were more than $25.