Fortunately, hoyas can handle the rubbing alcohol treatment! I have a big one (well, big for me, not compared to Lin's!) that has had mealies on & off for a year at least... it's hanging apart from my other plants, and when I notice the creepy crawlies have returned I spray it with 70% alcohol until it drips and rub it around all the surfaces my fingers can reach. Repeat a couple of times at 1-2 week intervals, and while I guess they're not totally gone at least they go into hiding.
With your hindu rope hoya, I wonder if you could make up a bucket of Neem oil solution (like a tablespoon or two in a gallon of warm water) and swish the stems/leaves around in that... don't know if Neem is as effective as rubbing alcohol, but... ?
