Hi,
I am not sure but i THINK that you can apply to register with the nursing board and then when you get that (approx 6 weeks) you apply to the ANMC for a MODIFIED skills assessment instead of the full one, I think for the 175 you need both and am not a 100% sure that the modified is suffice. Have you tried contacting the High Commission you can email them or phone , the number is 0906 550 8900 or
London.cc@dfat.gov.au. they are not always that brilliant at answering a range of questions so you have to ask for a yes , no scenario. Also you can usually blag one free question out of an agent.
Good luck
Kate