You can buy the rear taillight assembly that non-NA vehicles get. Since amber turn signals are required in the EU, they get an orange cover instead of a red one (all the bulbs are white). Installation on the E90 literally took 5 minutes, just detaching a wire connector then loosening the unit via 3 screws. Here are the part numbers for an E70:

63217200817 (left)
63217200818 (right)

Since there aren't many of the pre-LCI ones available on eBay.de, you could consider the OEM LCI taillight retrofit kit. Just buy one from Europe so you keep the orange turn signals. Some recoding is necessary but shouldn't be a hassle if BMW developed it.

63217227789 (left)
63217227790 (right)

You're not alone. Red blinkers annoy me but it's many automakers' way of cutting costs for North American models. Given how big the X5's taillights are though, it won't be cheap.

Rückleuchte, links BMW X5 (E70) xDrive30d von Bosch - 0 319 398 703