PC, Windows 10, TVNZ OnDemand app.

Works well, but eats up my RBI data cap too vigorously! What I really want is to make use of my generous off peak data allowance by downloading the programme over night to watch later (not to keep forever...). The official line is can't do this due to online rights obligations. However, given that if I had my act together I could have recorded the programme on my MySky box, it's hard to see the 'wrong' in what I desire.

Are there any known solutions to my problem out there?