Well, one asthma attack and a can of 3M Dust Remover later, I am sorry to have to report that the sunflower seed is now irretrievably entombed under the Enter key.
It was like an archeological dig at my desk. I worked away at my keyboard with the dust remover, aided by an eyebrow brush, a pair of tweezers, and a seam ripper. A ton of stuff came out of there--including a mat of fur large enough to cover half a cat...but no sunflower seed.
Worse, now all of the keys feel a bit harder to tap.
Well, I have to admit that I have apparently not learned my lesson about refraining from eating trail mix while online because now there is another sunflower seed in my keyboard.
...And that first seed from last year is still trapped somewhere under the Enter key.