Dear _____,
I find myself very busy lately. Can you be a sweetheart and surprise me with packed lunch one of these days? Or you can also invite me for a quick lunch. I promise, even though I'm busy I'll make time for our surprise lunch date. I know you're not that busy with work, or at least you have more control of your time simply because you're the boss. (sigh)
But if you really insist that I stop working because as you said earlier, what you have is MORE THAN ENOUGH for us, I just might. Please ask me again. Maybe, tonight?
Okay, gotta get back to work.