THAT is the perfect line....
I'm going out to get some coffee, want to come along?
Gee Whiz, I wish I was single so I could go try that one right now....It's perfect in it's simplicity.
However, if he says "no" and it appears he said it because he's getting ready to do something else, say "Well, maybe some other time, OK? I know this really great place."
THEN, shut your mouth to see what he says.
then, if he says ok, WHIP OUT your day planner and flip through 5 or 6 pages, say "OK, May 5 looks good....about 6:20?"
NO NO, don't do THAT!!!!