Just for the heck of it, I took a tape measure out to the XF and did some quick measurements. If they did offer a traditional T-top option, each "half" top would probably be at least 32"x24". I then checked the trunk, and even though you could probably get both sections in, the 32" length puts it right up against the back of the seat. I'm sure some industrious engineers could probably figure something out if they tried. Interesting concept though.
(good thing us "sports car types" travel light)