What worked for me was to kind of roll the toilet paper up like a cigarette (that's the only way I can think of it, non smoker here) and I think it took me 3 separate pieces. They still come out now and then but it's no problem for me. You could use some double sided tape and put it on the tops and bottom of the toilet paper to.
If that doesn't work, then I did hear that the dt250 pads fit, but you will lose some isolation.
The DT250 pads are made of velour, likely as comfy, or more comfy, but don't isolate as much. I also have heard that they push the mids back a little... Maybe that was with another headphone. Not sure.
Also I am not sure what are you are reffering to, I never said anything about switching them out during the winter and summer But if you do plan on doing that, I would assume the HM5 pads would be better for winter, they keep my ears nice and snugly
Another idea would be to try to reduce the clamping force so they aren't as pressed on your ears. I stretched mine over the box they came in (headphone box upright and front of it facing me) for 2-3 minutes and it decreased greatly.
I remember reading here that some people reported sound signature change with DT250 pads. Just one extra option to consider - Ultrasone Edition 9 pads are said to fit HFI-780 and are still available at some Ultrasone distributors, altho are pretty expensive - IIRC around 120 EUR here in Europe.