Hi Anthony,
You can whip the assist cord to the shank of the hook with a bobbin holder and waxed fly tying thread and then coat the threads a few times in clear nail polish or super glue. That's how I make all my assist hooks, this is how Owner do theirs and it is very strong if done correctly.
I usually bind the waxed thread to the shank below the eye for about 15-20mm a few layers thick to give some grip for the assist cord, then lay the assist down and whip the thread over the length of assist cord on the shank until you get a good tight hold a few layers thick, then finish it off with a pull through (similar to rod guide binding) or whipped finish as they do for fly tying and trim, then give the thread a good coat.
Hope this helps,
Cheers,
Ian