So simple it's silly: Gift Idea - Auto Reloaded G-Gift Cards At Starbucks.

From the "Why didn't I think of that?" file, you can totally re-load someone else's Starbucks card, given that you have their card number.  I just got this from another website, where in lieu of a "tip" jar, she had a "fill my cup" link, and of course I followed it. 

Not a good idea for me, because, I'm So Not Able To Get There Or Anywhere, but I have had my share of homemade cappuccino in the last week.  But, for you it's a great idea!