Just point your scope to the south pole so the digital setting circles read -90 S, that aut to get you close enough.
i dont know if your bellow or above the pole, but if for example your bellow the pole, so you need to raise the alt axis, then slew the scope south (check your going the right way by looking at the NSEW cross in the top right of the window), you can gauge your movement by measuring out 80 arcmin with the angular separation tool. Then, as you know, try to get back to that same place with plate solves before and after.
Having said this, PA doesn't need to be spot on, there is no spot on PA for your rig. There will be different PA for different aspects of the imaging system you want to optimize. And, Protrack will compensate for some miss PA.
You may find it easier to do a new large tpoint model and use that. Sorry if ive covered what you already know.
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Josh