Get a different seat, like the britax marathon. Should fit just fine. See this edmunds fit test and commments. http://blogs.insideline.com/roadtest...ment-test.html
I looked at that fit test before buying the x3.
2013 X3 28i, AW, Chestnut, Sienna, ZAP, ZCV, ZCW, ZDH, ZPP, DHP, rear view, park distance, cargo net (Wife's)
2010 Porsche Boxster S (Mine)