I've seen it done. ID like to install some Halo LEDs onto my 1971 duster but I still have the original sealed halogen bulbs. Does anybody have a headlight they use that isn't sealed, I can open and install it onto my duster?
I did it, then I grew out of it. Eventually some of the led's just blinked out of existance. They sell the actual lamps with led's built into them on ebay. That's where I got them, $30 or something a pair. The lamps themselves illuminated poorly as well. For the turn signal/park lamps I wrapped small LED strips into the housing and glued them, and wired them to the same switch as the Halos. You're better off making them by baking a set of Hella's in the oven and putting an led strip in it. Actual 7" halo rings would be a way better option though if you're going for that BMW look.
That's what the lamps I used looked like off:
and all on:
The leds don't give the right effect I think you're looking for so I'd go for something else. Like a 7" CFL. That's what gives that solid color appearance. Then set it up as a DRL, that's how i had mine, and they turned off when you switched on the headlight.
On Ebay there are a ton of 7" round Halo headlights, pick the color you want and go. Only thing is some aren't DOT approved. Here is a thread from when I thought of running Halos http://www.forabodiesonly.com/mopar/showthread.php?t=291637