No, have never done Kosiosko. So you would be one up on us there! On a serious note the best training we did was Mt Coolum on the Sunshine Coast. This little bump has some pretty steep going and repeat climbs of it, in my opinion, were definitely helpful. The other thing was just walking for 5-7 hours at a time, up as many hills as you can find with a pack on.
A lot of our training was done in National Parks and walking in the bush was the best therapy for me recovering from chemo, radio and learning to live with hormone therapy side effects! Something about being in the natural environment, wherever you are, just does you good. :)
Hope that the rest of your treatment goes quickly and you are soon enjoying life again too! xox