This is not to discount the other meanings, but here's one that's been overlooked, it seems:
Noun:
1) The act of fixing or building something by tinkering, prodding, poking, and twiddling it until it looks the way it should or does what it ought to do. The act of solving a problem in a very make-shift, seat-of-the-pants way rather than proceeding with any sort of plan or forethought. Jiggery-pokery is all about "Good enough"
2) A very informal, vague process for doing a thing - there's no step-by-step thing you do to get the result you want, you just apply the jiggery-pokery until it starts making the noise and doing the thing
Possibly, this comes from literally "jiggering" (jiggling) and "pokering" (poking) a thing until it comes together or starts to work or both.
1) I just used a bit of jiggery-pokery and I got your phone working again; I majored in jiggery-pokery in college, I did.
2) Careful with the coffee machine - you need a bit of jiggery-pokery to get it working.