I've once done a parapente intro day, where they used a winch as well. One of the techniques they used to gain additional height was a stepped launch, where you would be winch-launched as normal. But at the point where you would normally let go of the wire, they gave you slack so that you could turn around, fly the length of the field (and then some) back, turn around once more, and get winched in for some more height gain. This could go on essentially indefinitely (until the wire would run out), although after a while you needed to be really careful or otherwise the wire would get tangled in the barbed wire and the trees that separated the launch field from the surrounding fields.
Do they do this with gliders too? Or is this impossible due to the way the coupling mechanism is designed?