John, I've done it in my 10" Dob, but using an off axis aperture mask. I made it from a piece of card stock & cut an 80 mm hole near the edge, so that it cleared the secondary. Tape to top of tube making sure that it also clears the spider. The seeing has to be pretty good, as this mask increases your f ratio. Mine goes from 4.5 to 14.25. It gives heaps of contrast & you have to use a fair amount of mag. (200X ++). Another trick, is to cut slightly smaller than 80 mm, square, hexagonal, triangular holes in card stock & cover the off axis mask 80 mm hole with the shaped mask. These 'flat masks' are then rotated, which also rotates the diffraction spikes, ie; moving them out of the way, allowing you to see the companion. This is probably best done by an assistant.
It's best tried when somewhere near zenith & on a good seeing night. Otherwise the flaring will negate the exercise.
I've tried doing a similar thing with Sirius, but without success. Too bright & too close to each other. Need more aperture. I've seen it in a 14" SCT a few years ago, when they were slightly further apart.
This will really test your collimation as well.
HTH.
L.