I would probably tie a half-hitch loop in the leader, and then with the loop coming out I would pass the *whole loop* through the eye of the hook on my hopper and over the back of the fly and then tighten it so the loop cinches up against the eye. That will give you a “snell” connection; basically a loop to loop knot using the eye of the hook as one “loop.”
If you want to move the hopper, you should be able to tease the loop back open by wetting the connection and holding the line-side tippet while gently tugging on the fly. Then un-loop it and re-tie wherever you want to put it. This is how my balloon indicators are attached and I move them this way as well.
Zach