DOT fluid is only for hope brakes. Magura discs use mineral oil. I bled the disc on my mod with water years ago and it was fine. At one point I even used a HS 33 lever and it still worked fine the lever just felt stiff. I can't remember exactly how I did it but I'm pretty sure I used a syringe and bled from the caliper up to the lever. Its not the best idea to use water with a disc brake but it does work. I didn't notice the water getting hot, expanding or boiling when I did it so I think you'll be alright for trials. Don't forget that you'll have no warranty if you do it though.