Absolutely, it will be possible to use a relay, in fact that's my preference. Personally if I were you, since you have HID headlights I wouldn't mix standard halogens with your fog lights. Granted, it will look like a euro car with that setup but, it's just not my style. What I did was buy some projector fog lights and did a retrofit and put HID's in my fog lights too. All in all, by the time I spent the money on the projectors, the relay harness, the HID kit and about $3 in nuts/bolts and L brackets from Ace hardware... I think it came out to be about the same price or maybe a little less than what the price would be for OEM fog lights. It took a little bit more work because I REALLY took my time to get it perfect, but in the end it was well worth it and much cooler.
Something to keep in mind is that the OEM fog lights are prone to some issues. The housings tend to leak and let moisture in. The insides can often get too hot and the reflective surface get ruined, etc. It's kind of a luck of the draw type deal. If you ever are in a parking lot and see a 9g take a look at the fogs. About half the ones I see at least one of the fog lights is discolored because you can tell it burned out from moisture and overheating... etc. So, like I said, luck of the draw.
Here's a couple photos of the retrofit I did.
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