Sorry, but you're wrong there. Remanent magnetism will allow you to use an AC induction motor as a generator just fine.

Absent any remaining magnetism you can 'flash' the motor core with a short DC pulse and then start rotating it with your chosen driver afterwards.

Just one sample (of many) of people using this trick for all kinds of interesting small RE applications:

http://www.smallhydropower.com/induction.htm