Personally, I think you're seriously messing up your priorities. With things which are normal (long settlement, paying deposits, etc) you see snake pits around every corner. Things that might be real problems (unfinished pool, structuring the loan, deadlines) you're dismissing out of hand.
Assuming you are redrawng from the PPOR loan (and not taking money out of an offset) the interest on the amount you redraw will be deductible, so it doesn't matter if you draw more from the PPOR loan and take a smaller mortgage on the IP. The interest deduction will be the same.
HOWEVER, because your PPOR loan is now mixed deductible / non-deductible, interest has to be apportioned. Gets complicated, as Rolf said, if it's P&I because you have to apportion the principal repayments as well.