Just saw your post, thanks for the info. I'm a little confused about how to get both the flash synch chord and the shutter remote wires through a single bulkhead. Is the idea that you use all 5 pins on the bulkhead, 3 go to the remote shutter, and 2 go to the flash synch cable? I can see how this could work, but I'm unsure of how the dual synch cable fits into the equation. With a dual synch, wouldn't the two cables outside the housing converge to share the same 5 pins on the bulkhead--seems this would prevent me from having them diverge again to go to shutter/hotshoe inside the housing.
I only need to be about 5 ft. deep... I might just put one of my old SLR's in a pelican case with a 4x4" glass filter set in the side for a lens port and cable glands to pass the shutter/flash synch chords. This is my setup for camera traps topside and I'd think it'd work underwater.
I used the second option on my Hugyfot housing using one of the Nikonos penetrators (Ikelite in your case I believe, but it is the same deal), these have five pins plenty enough for the remote release. On the housing inside I belled out the connections with a multi meter and spliced the ribbon cable into the N3 three pin plug used by Canon. (Pinouts found here http://martybugs.net...Connector.html)
I then butchered a dead sync cable for the Nikonos plug and spliced a cable that was long enough into a second hand remote release that I had. Jobs a goodun.
As for remaining flash capability I have three Nikonos bulkhead connectors on my housing, but if I had only one I would have used a dual sync cable.
Overall this is much better than drilling a new hole as aside from have to tap the thread for the new bulkhead connector you would need to machine a recess for the oring. It a job of fairly low tolerances and one I would feel uncomfortable doing with the correct tooling (press drill, etc). If you where to go down that route a trip to a maching job might be in order.