Creating has_many relationships in ActiveRecord without :primary_key

I'm working with an older version of Rails and ActiveRecord that does not have the :primary_key option in has_many relationships of more recent ActiveRecord versions and unfortunately I don't get to control when we upgrade. Is there any way to hack this s开发者_JAVA百科olution via :conditions or :finder_sql options?

It should be possible using :finder_sql e.g.

has_many :foobars, :finder_sql => 'select * from table where foreign_key = #{primary_key}'

Note the use of single quotes around the query so that #{primary_key} is not expanded at the time when the association is declared.