Would something like the Fake_arel gem help?
Fake_arel
simulates and supports a variety of features from Rails 3 for earlier Rails versions. The only major requirement is that your currently-used ActiveRecord gem needs to be greater than or equal to version 2.3.5.
The documentation also notes that Fake_arel
can be used as a bridge between Rails 2 and Rails 3 apps, which could ease future transitions to later Rails versions.