If a manual solution is what you're after, I'm thinking a long, could be several feet in length if needed, piece of thick, smooth wire rod really, like quarter inch diameter, would allow you to stand outside the run, yet by pushing or pulling the rod, open and close the horizontal door.
If it was real long, just support it every few feet with screw in eyes, or an eye that hangs from something overhead, like framing, a tree limb, wire over the run, anything really that you could hang an small metal eye from.
I don't know your setup, but a smooth quarter inch rod came to my mind. You could bend a handle one end, and a hook on the other, to hook into an eye on your door.
There's metal supply houses that will have long lengths, probably up to 20 foot, although at real long lengths, maybe over six feet, those support eyes become important to carry it, but also keeping it from bending the rod, when pushing the rod. You can probably grab shorter lengths at Tractor Supply, or a Home Depot type place.
I am on it!
