module Middleman::Base::ClassMethods

def set(option, value = (not_set = true), ignore_setter = false, &block)

Specifically for the asset_host feature
Override Sinatra's set to accept a block 
def set(option, value = (not_set = true), ignore_setter = false, &block)
  if block_given?
    value = Proc.new { block }
  end

  super(option, value, ignore_setter, &nil)
end