1. Eat Magic Eater.
2. Get a debuff that transforms you into a critter.
3. Get flag.
4. RUN! (you can also use Pots, Rocket Boots, other speeding up stuff while even in the critter form).
iirc the speed increase in the critter debuff form is 100%
Note that even under the debuff, it may not give you the speed. Happens rarely; in that case, repeat steps 1 and 2.
Noticed it today while waiting for party (; Then went WSG and it worked.
EDIT: If you drink Noggenfogger to become smaller, then transform into a cockroach, the flag will scale too and will be very small, and hard to notice!