yep you sure can!
DX6i (Student)
Bind model, establish correct trim settings
Set 100% rates
NO EXPO ON STUDENT UNIT
Plug trainer cord in, leave power switch off
DX8 (Instructor)
Bind model
Set DR to whatever desired
Set expo as desired
In system setup menu, set Trainer mode to Pilot Link Master
Trainer cord in, power switch ON
Adjust the trims on the STUDENT tx so that with the sticks in neutral,the servos don't jump (much) when switching between student and master.
The master radio will read the signals from the trainer as if they came in on its own sticks, and it does all the D/R, Expo, and mixing based upon the instructor's radio.
In Programmable Master you need to do the mixing, trims, etc. Then the master can disallow control of individual servos from the student. This is really easy to do when using two DX8's because you can just copy the model over via the SD card.