That sucks. I have had neck surgery from a car wreck injury vertibrae fused. I have pinched nerves in my arms that mess me up. I have good days and bad days. I am all about doing things the easier way now.
I found with this method that the key is to spray it on every day and let it soak in over a week maybe weeks on the thicker stuff. Get a thin flexible steel paint scraper and put a sharp edge on it. The wd40 makes the undercoat really flexible and release its grip easily. Some of the harder deposits i have had to use a portable bernsomatic torch to warm up the undercoat then scrape it off.
If you can get wide rolls of auto body paper id recommend rolling it out on your garage floor under your car to catch the dripping wd40, and all the undercoat scrapings then you can just ball it all up and toss it into the dumpster.