It can use erb tag on configuration.yml.

lib/redmine/configuration.rb

@@ -81,7 +81,8 @@ def with(settings)
       def load_from_yaml(filename, env)
         yaml = nil
         begin
-          yaml = YAML::load_file(filename)
+          body = File.read(filename)
+          yaml = YAML::load(Erubis::Eruby.new(body).evaluate)
         rescue ArgumentError
           $stderr.puts "Your Redmine configuration file located at #{filename} is not a valid YAML file and could not be loaded."
           exit 1

test/fixtures/configuration/erb.yml

@@ -0,0 +1,2 @@
+default:
+  somesetting: <%= ENV['somesetting'] %>

test/unit/lib/redmine/configuration_test.rb

@@ -41,6 +41,12 @@ def test_overrides
     assert_equal 'bar', @conf['somesetting']
   end
 
+  def test_use_erb
+    ENV['somesetting'] = 'foobar'
+    load_conf('erb.yml', 'test')
+    assert_equal ENV['somesetting'], @conf['somesetting']
+  end
+
   def test_with
     load_conf('default.yml', 'test')
     assert_equal 'foo', @conf['somesetting']