I know a couple of very good sevens ones, which might be able to be converted to 15s...
1) Have the scrum half at the spot, with his back to the opposition. Winger and centre are on opposite wings, way out. The remaining players are in single file. The scrum half points discreetly in the direction of the attack and taps the ball. The line fans out on the right side. If the opposition winger gets sucked in, use a miss to the wing, if not, there should be huge gaps in the middle.
2) Have the two halfbacks where the penalty is, and the other players on the other side of the pitch. when the ball is tapped, the other players fall on the ground, scream and writhe about. The opposition should just look at them with a "WTF???" expression and you can just waltz through and score. This could be brilliant or go horribly horribly wrong...