gistfile1.rb

# option 1
info = CustomInfo.new(:keyname => params[:keyname], :value => params[:value])
info.informable = @informable
info.save!

# option 2
CustomInfo.create!(:keyname => params[:keyname], 
                   :value => params[:value], 
                   :informable_type => params[:informable_type], 
                   :informable_id => params[:informable_id]
                  )

#option 3
@informable.custom_info.create!(:keyname => params[:keyname], :value => params[:value])