It can be done, but each SUV / tandem combination are a little different. The one's with fold-flat seats and a low or no center console will sometimes take a tandem with only the front wheel removed such that the rear wheel ends up sitting in between the two front seats. On SUV's like Debbie's '95 4 Runner where the rear bench folds forward and creates "retaining wall" between the cargo bed and the front seats, we can remove both wheels and flip the tandem upside down such that the rear triangle / rear derailleur sits just abreast of the headrests. We put foam kayak roof blocks under the stoker's handlebars to stablize the bike and ran cargo straps from the captain's cranks to the floor tie-downs to hold it in place.

Best bet is to take a tape measure to your X-5 and to your tandem to see what will and what won't work. I try to avoid laying tandems flat on one side in any vehicle because: a) it takes up too much cargo room and, b) it's a pain to move them in and out as the cranks hang-up on the floor unless you put them on top of a large piece of cardboard (bike box) and then slide the tandem in and out with the cardboard under it.