To fix this:

1) Nitter offers a deal: download our browser extension, sign up for Twitter, and we'll give you some kind of perk (Amazon credits, whatever).

2) Browser extension surfs Twitter on the user's behalf, scraping and sending copies to Nitter.

3) We find out how serious the legal system is about prosecuting scraping.

The whole point is not signing up for twitter. If signing up for twitter wasn't a problem, Nitter wouldn't exist in the first place.