I went for funny (and no hint of anything that might rub the guilt bone). Now, I don't give him a card. We all go out to eat someplace and I pick up the tab. I say "Happy Father's Day" and have been known to give him a hug. I get why you like the card, I get why it may make him feel bad.
Also, if you're like me at all (I'm a talker), and he's talking, and you are listening.....turn your body towards him, look him in the eyes and really work at not speaking.
I have to tell you that at first, sometimes I didn't really hear what he said b/c my mantra was "shut up, focus, shut up, focus". Ok, I really did hear and I would say validate, just sayin'.
Because I am a talker though, I will not interupt to validate (if I slip, I apologize and ask him to continue) I work really hard at not interjecting anything and I will find different ways of showing my appreciation for his being able to share with me. Sometimes it is verbal and sometimes it is a squeeze on the arm.