Macho, masculine guys are never supplicant. They never dream or hope to kneel down in front of a guy to show their ability at serving cock. They don't hope to feel the warm burst of cum splashing on their face or inside their mouth.
Remember make-off, sissy? Your assignment is very similar, with some key differences.
You've got another chance to practice your perfect, feminine make-up. You'll certainly want a minimum of lipstick (or gloss), blush, eyeshadow and something a bit more enduring like eyeliner or mascara. Be sure to give your inner sissy the time she deserves, and don't feel obligated rush to get the make-up off.
Now you're going to discover a new use for cum: as a make-up remover.
That's right, you're going to cum or (if you're a very lucky sissy) use someone else's cum to clean off your face. And to help you stay true to your assignment, you must ruin your first orgasm. That way you'll have some cum to work with and you have a better chance of controlling your bothersome other half.
(If you're not familiar with "ruining" an orgasm, this is when you stop stroking your clitty the moment before you cum. Stroke until an instant before you orgasm and then take your hand away. You'll still cum, but it will not be your usual orgasm.)
All you may use to clean off your make-up for the next 24 hours is cum. And you'll have another wonderful use for cum. It's certainly not the most healthful or efficient use of cum (and some sissies may need to ask permission if their mistress has ordered them to drink every drop), but every sissy need to experience the feeling of having dried cum all over her face (and if you might happen to need to explain why you're wearing eyeliner and why you so obviously smell like cum, that's just a side benefit).
You can always elect to not try cleaning off your make-up for the day. Cum getting in your eyes does sting, after all.
(And, as before: safety first. Even if you're cowardly male side is desperate to clean off your make-up, be very careful about rubbing your eyes. They can take the pH change from cum easily (even if it stings), but rubbing bits of powder or dust under your eyelids inadvertently when wiping your eyes can be harmful)