Me, I'd just use pitch/ varispeed/offset/fade to simulate bleedthrough. I wouldn't worry about the almost imperceptible impact of the diameter of the adjacent tape layer.
Working in studios since the late 70's, I consider it a bad thing. I'm sure there have been some cool artistic tape bleed accidents, though the only one I can recall was a Led Zeppelin track.
Heh. Now trying it on something is on my to-do list, darn it. O.o
