I use the 10mm Superbright LEDS in custom interiors all the time, all I do is grind down the dome flat to just below the dome starts and leave the ground surface as is. This changes the output of the LED from a near perfect 2-3" circle with a very definate line to a soft light that just blends out, its very hard to descibe sort of like fluffly clouds. I will takle some pics of the 63 Cadillac I am doing at the moment when I get back home later.

Cheers Angelo