UPDATE: v-leds.com emailed me back to say that they have some that are non polarity specific, with a little black box (bridge rectifier) mounted on the PCB. Turned out two of the four bulbs I was shipped have this -- and, indeed, they worked with the correct side facing down.
So, if you order these bulbs, make sure you specify that you need the non-polarity specific ones!
So, if you order these bulbs, make sure you specify that you need the non-polarity specific ones!