Or is the best alternative to use the ModelName.validators method mixed with some ajax, and do the validation through the jquery-validation-rails gem?
From the Google.
Also this guy seemed to have gotten the same gem you are using to work by using the 4-0-beta branch.
If the 4-0-beta branch works for you, consider helping to maintain the gem to keep it alive.
To use a certain git repo version in your Gemfile:
gem 'client-side-validations', :git => 'https://github.com/bcardarella/client_side_validations/tree/4-0-beta'