My assiduous research has paid off! Angela has just revealed some of the secret lore of the second circle of the Art Of Using Safety Pins.
How to Use Safety Pins and String to hold up a tucked out blouse, while maintaining the illusion that it is tucked in unless one has a more than cursory look:
1. Tuck out your blouse
2. Fold it to desired length
3. Pin Safety Pins in 2-4 strategic locations ("safety pins at the ends... (at the waist and at the hem of the erm.. blouse)")
4. Thread string/thread through to hold the folds up
This does seem like a lot of trouble to go to. And it's still detectable, albeit much less. Anyhow, if you get careless and the metal of the safety pin can be seen from the outside (as did the J1 girl I saw that day and the former CHIJ girl who got busted by David Liew for wearing her CHIJ blouse instead of the purple uniform) (it's supposed to pin through the fold, not out of it), you will face doom!