You also could most likely get away with secondary and tertiary strobes. ;)
So let's say you're going to block the SB-27 from exposing the scene.
The SB-800 becomes your key light.
From all said above it will get wirelessly shut off by watching the SB-27 which will get shut off by watching the film. We all agree on that so far.
Recall that film-TTL flash (and the d-TTL flash which briefly followed it) were crude. Much like the auto mode on a thyristor flash they looked for the quantity of light with one (or very few) sensors. Unlike the beautiful matrix-meter-powered flash exposure system (i-TTL) of today.
SOOO... Theory:
If you add a second and third DUMB slave (some $10 optical triggers) they should work and be counted so long as they provide an insignificant part of the total light and are set in manual mode with a duration shorter than the SB-27 and SB-800 will have.
Example:
SB-27 on camera in (film)TTL mode.
SB-800 as key through beauty dish on face.
Dark background.
SB-XX set to manual mode, on $10 optical trigger 1/16th power, right side rim/hair light.
SB-XX #2 set to manual mode, on $10 optical trigger 1/16th power, left side rim/hair light.
So long as the brains of the system (F90 / SB-27) leaves the SB-27 on for longer than 1/16th duration this should work.
The 27 will fire, the 800 will see the 27 and fire in unison, the $10 triggers will see those two and fire in unison, the F90 will be quantifying all the light coming in, the two SB-XXs will finish their 1/16th job, the 800 and 27 will continue, the F90 will quench the 27, the 800 will see the 27 quenched and stop itself.
I don't think these dumb slaves are as likely to work as backdrop lights because then they will be contributing a much more significant percentage of the total exposure and the odds of them running longer than the controlled strobes is higher.
