So, what turned out to be the best solution for me was to use a hex editor (as suggested by user60561).
Apparantly, the name of every function and field is only saved once in the class file so if you use names with the same amount of bytes you can hexedit your way to victory. For me it came down to replacing "new" by "abc" and every strange unicode character with a two-char sequence.
Thanks for all the suggestions.