You stated, 1 to 2 times per week handling?
I handle mine probably 4 or 5 times weekly, (almost every day) except for right after feeding which is currently every 10th day.
When "handling" what do you do? Sit there and hold the snake? You did not specify. I take him out of the cage, place him around my neck, clean out his water bowl and add fresh water, (he gets to watch and help). Today we went to the park together, and he climbed on the fence posts, crawled on the ground, got to pose for pictures from "Curious Onlookers." etc....
In other words, I don't just take him out of his cage, hold him a minute or two and put him back.
When I handle Rufus, it's more like an hour or so at a time. He's quite used to spending time with me and seems to enjoy it. I even ride down the street with him around my neck and he does just fine.
Having said all this, let me now tell you, He is 4 years old and I have had him since he was about 6 months old. He was quite "Flighty" (as you've stated) way back then, and was nowhere near long enough to wrap around my neck.
The answer is: It takes time, lots of time, and lots of handling. The more the better.
You did not state if your snake is a baby or an adult. There are pros and cons to both.
If your snake is a baby, it's perfectly normal for them to be nervous, shy, scared and flighty. He may grow out of it with lots of handling like my snake did.
On the other hand, if your snake is full grown and still this way, You know the old saying, "It's hard to teach an old dog a new trick." Some snakes that grow to adulthood without proper handling and that are abused or neglected, may never become the "Lap Dog" you'd like them to be.
I'm including a short video clip (link below) of me and my snake goofing around one morning:
https://www.youtube.com/watch?v=h_6b...ature=youtu.be