This man has the right idea. This, or any of a hundred related phrases. I would add two instances of the word "fucking" to that sentence, and then add a couple of exclamation points,
and I think it's just about perfect. Wait. Let's change 'mouth' to 'face' and 'in' to 'on'. That leaves us with:
"Please fucking cum on my fucking face!!"
Said in what one imagines is a tone of brutal, hollow, cumdump desperation.
Perfect.
-IC