| My question is this: is there a way to turn off the TFT display via some
| power-management function, or even just turn it off at the OK prompt so
| the machine boots without a display?

Most drivers for Sun frame buffers support an ioctl() to blank the display.
This is issued either by the X server or screenblank(1).  However, some 
drivers do not implement this correctly and generate a black image rather
than turning off the signal to the display.  If that's the case then the
drivers may need a bit of tweaking to make that work properly.

Eduardo