There's a reason why the dice have to hit the backboard in casinos. Throw a die against a hard surface and then tell me you can manipulate the results. Coins are the same thing. If a coin hits the table, it will bounce, unless it's a cheap plastic TPCi coin, which I will not use.
Not to totally take this off topic, but...
It's not impossible. I was watching a documentary on the Discovery Channel (or maybe the Travel Channel, I can't remember) on this guy who developed a dice throwing technique to roll 7's and 11's.
The documentary went on to show him developing his technique as he perfected throwing angle and power. Later on, he even gave people classes on how to do it.
Basically, he would grab the dice with 7 facing up, but I'm not sure if it was 5-2, 6-1, or 4-3 (one combination of the columns on a pair of dice has more numbers that can add up to exactly 7, but I forget which one. This comes into play later). He held the one on the left with his thumb, and the one on his right with his middle finger, with his index finger bracing the front of the two in the middle where they meet. He used an underhand swing and used the physics of the dice hitting the backboard to bounce them back onto the correct numbers. The dice don't go wild, they roll perfectly in the air, and continue even after hitting the backboard. Basically like a square wheel spinning in the air and hitting a wall, which knocks it back on its other side.
Of course, this is severe manipulation of the dice. I don't really think this technique can be used in Pokemon since you only roll one die, there is no backboard, and the fact that an underhand swig would easily miss the table and that we aren't aiming for 7's and 11's. I hope this doesn't get deleted....