I line dry mine, and then just tumble with a wet tea towel or something for 10 mins or so on hot to soften them up. I find using the wet towel works better than just doing it with the dry nappies. You can try and get them off the line before they are bone dry and finish in the dryer, but I cannot seem to time that. My nappies are either wet or bone dry (here in Houston!)
could you try angling the velcro so that the legs are a bit looser? also a barrier cream on the area might help to prevent the rubbing something like vaseline (just a thin layer so nappy not affected)? Only other idea i can think of would be to fasten them looser and use nippa to pull in the waist???