Can I contribute without being an US citizen?
It seems to be an US-internal issue, but considering that most of the net belongs to the US, this might actually be a far more global question than is legally coverable/definable by US law.
Good question. You could donate to the ACLU or Fight For the Future.
Also, certainly being active online and discussing it openly helps.
I think you'd want to refrain from commenting on the FCC website or otherwise pretending to be American. While there are anti-NN folks doing impersonation, it's not a good behavior to copy.