If you make the display 12 redstone torches in a row, just make the first 2 dummies that stay on and make a random 10-roll. That'll make it at least 2 and 12 or less.
I saw something that created a random output with the use of cactus. When the cactus grew, the top fell off and the item landed on a pressure plate. You could use this idea, but it isn't very reliable.
What could be better is a bunch of and gates though. The clock will have various outputs all attached to their own and gate. When a given out put is on, and a button is pushed, the output of the and gate will turn on. Due to the length of a button press to be .9 seconds (I think) you would have to put a pulse limiter on the button. This will prevent the button from activating two sections and giving you two outputs. You may wish to assign each output to a memory cell so it will remember the number for you. You can then have the press of the button attached to the reset piece of the memory cell so it clears the memory every time you 'roll' the system.