If you're willing to throw the dice a bit, and you wouldn't consider this a tainting factor (no sarcasm), contact Starbucks. There's a distinct possibility they may work with you. Depending on how you judge the risk, you may want to do this anyhow, lest they simply shut the card down entirely in the near future. There is of course the risk that contacting them may cause that result sooner, but... in the long term you're probably better off contacting them anyhow because if they're going to shut it down when you bring it to their attention, they're going to shut it down when they discover it anyhow. I think you still come out ahead in the case where you contact them and they end up not shutting it down when they would have if you didn't contact them.

Otherwise, you're "stuck"; be open about it (as you are), and use them or not. I wouldn't hold it against you either way, personally.