gistfile1.rb

class SomeStatsModel < ActiveRecord::Base
  establish_connection "that_other_stats_db_#{Rails.env}".to_sym
  TABLE_NAME = 'some_oddly_named_stats_table'
  self.table_name = "some_default_schema.#{TABLE_NAME}"

  def self.sum_select(*args)
    self.select(*args.map {|s| "SUM(#{s}) AS #{s}"}.join(', '))
  end

  def self.for(account_specific_schema)
    klass = Object.const_set("#{self.to_s}_#{key}", Class.new(self))
    klass.table_name = "#{account_specific_schema}.#{TABLE_NAME}"
    klass
  end

end

gistfile2.rb

SomeStatsModel.for('account_xyz123').select(:app).sum_select(:requests).
    where(date: Date.today - 2.days).group(:app).order('requests desc').limit(5)