Using the command

/setblock x y z minecraft:hopper[enabled=false]

creates an invisible ghost-block.

The ghost-block causes buggy collisions if placed in air and only appears normally if you exit and enter the world again. If placed in a normal block, it only appears when you try to interact with said block, at which point the hopper GUI pops up and the hopper block becomes "solid" like normal. The ghost block prevents pistons pushing, like a normal hopper block should.

If the hopper is placed adjacent to a power source, the ghost-block is not created, and everything happens like normal.