Chaining scopes with OR instead of AND

I have an advanced search method which chains a bunch of named scopes
depending on an options hash. It is similar to the anonymous scopes
railscast from awhile back, and it works great.

However, the resulting query always joins the conditions with AND. Is
there a way to chain named scopes with OR instead of AND in Rails 2.3?
Or perhaps ActiveRelation in Rails 3 will somehow make this possible?

Thanks for any assistance.