I am using the Spark in a commercial product, and what I did was to use an existing case, and place the Spark in it. It really works for me. The case I chose had a facia allowing me to have hidden holes for Reset and Mode. I used a BIVAR PLP5-125 Light Pipe to get the RGB LED to the front panel.
The Light Pipe is not cheap at about $0.60, but it has the look of a real 5mm LED, which was essential in my case.
As an aside, the one issue with using the Spark in a product is the Mode button. I know I can reprogram the code to allow Mode to work on one of the external pins, but I would rather keep things stock standard. Pity there is not an API that allows me to define in Flash an external Mode button.
Until then, I will rely on the small external holes. Where that does not work, I am looking at placing a small wire from the Mode switch to one of the external pins. I know this is a hack, bit it is a reliable one, subject to my expert soldering skills