Glad you liked my suggestion. Yeah, I think a Spock something or other would be cool. You should definitely do your eyebrows, if nothing else. That would freak him out for sure! I already have Spock eyebrows, so my husband couldn't tell the difference.
I actually got my husband to dress like a pirate for the midnight showing of Pirates of the Caribbean 2 (several of our friends dressed up as well). But I haven't really been a Fan enough about anything since then that I've really wanted to dress up (and if I'm not dressing up, he definitely isn't).
Hope you're able to come up with something really cool!