How are you measuring the humidity? 99% is tough to get unless it's a tub with only a couple of holes. If it's a dial type I would replace it with digital.
If you have not tried this give it a shot.
Use a well dampened pillow case and put the snake in. Tie the pillow case up and let him start cruising through it. You can gently rub around his head and body. This will usually work. I advise against the whole tape thing if it can be avoided as you can cause damage to the eye. Good luck.