As I'm currently aware of there has never been a case where a civilian has ever rode along in an SR-71 while in flight not even the president. Only about 140 of the finest hand picked officers at the time had the opportunity to do so. The SR-71 was treated much the same way as the space shuttle. Only trained personnel only. And now that its retired it looks like no one will unfortunately.
Here's an interesting video that even brings up the enormous fuel loss prior to flight. (look at 5:54)