The small blue "spot lamp" came in today. So I pulled out the map/dome light unit and found the right hookup for the spot lamp. Hooked 'er up and bam... got the blue mood lighting over the cupholder and gear shifter. Niiiice!
If anybody else is interested in doing the same for their 2012 Mazda3 then you'll need part number BCN8-69-974. I purchased mine from Smith Haven Automotive Group for $20.45 plus shipping. They were quick and helpful.
Now... time for the footwell lights.