From a powered point of view sorry to say I am afraid there isn't an easy answer.
If you are "just" worried from the point of view of the glider surviving all I can say is there will be a very healthy margin between the approved G limits and those the glider is actually capable off - it will not fall apart.
If you are worried for yourself, negative G tolerance only comes with pulling G and is lost, if not quite as quickly, when you stop. Obviously being in good physical shape really does help a lot.
I wish there was a simple answer and if anyone else has one I would love to hear it.