I was thinking that maybe an over center lever style jack (kickup style?) like the old Indy cars or racing motorcycles use. Prop it under the frame, step on the lever to lift and it locks in the lifted position due to going "over toggle", stuff your existing pony wheel under your existing jack and crank away. Once the existing tongue jack lifts off of the lever, pick it up off of the ground and walk away.
Nothing to modify so your classic camper stays original, and only a thin light device that could stow virtually anywhere. Might even be pressed into double duty for a lantern stand or tire change jack if you design ahead for it.
Think like the Egytians, leverage is your friend!

Well, I see now that you have no jack at all, so let me revise that. Stick it under, step on it to lift trailer off hitch, move car, lift light long end of lever to set back on pony wheel?
Maybe not as practical as I first thought.
