Yep, flip the tape's my vote..we used to flip the reel, record the backwards part to another machine. Then flip the first tape to it's first position, hand-rock the 2nd machine to where it needed to be, start both machines (one in record) and then fly the part back to the first machine. It was a real drag..hard to sync anything other than random fly-in parts, interrupted the creative flow because you (me anyway) had to blow a bunch of time just to see if it would add anything interesting to the song. It's so much easier now.
We used to do it with reverb sends and tails also. That backward reverb thing on a "front-ward" signal was sometimes interesting.