Finally have some time on hands, here are some details:
Foil looks like this, the upper one is clipped on the edges to fit under the filter, snowflake one; the other one is double-smiley, still intact.
This is what they produce on my bedroom wall with the same yellow LEDs taped to it:
And here is the setup E-sketch (top view first, then side view):
Only thing not on the sketch, I used a DIY snoot to direct the light to the paper, after experimenting with how to light the cup, the ones with this setup worked the best, but also had to use some ambient light (kitchen light to the right is on, too bad I didn't turn on something on the left side as well). The idea was to avoid my room reflecting on the front side of the cup.
Thanks people, appreciated!