diff --git a/scripts/arcanist.php b/scripts/arcanist.php
--- a/scripts/arcanist.php
+++ b/scripts/arcanist.php
@@ -165,6 +165,7 @@
   $workflow->setCommand($command);
   $workflow->setWorkingDirectory($working_directory);
   $workflow->parseArguments($args);
+  $workflow->applyRuntimeConfiguration();
 
   // Write the command into the environment so that scripts (for example, local
   // Git commit hooks) can detect that they're being run via `arc` and change
diff --git a/src/workflow/ArcanistBaseWorkflow.php b/src/workflow/ArcanistBaseWorkflow.php
--- a/src/workflow/ArcanistBaseWorkflow.php
+++ b/src/workflow/ArcanistBaseWorkflow.php
@@ -594,9 +594,32 @@
     $arc_config = $this->getArcanistConfiguration();
     $command = $this->getCommand();
     $spec += $arc_config->getCustomArgumentsForCommand($command);
+    $spec += $this->getGlobalArguments();
+
     return $spec;
   }
 
+  final function getGlobalArguments() {
+    return array(
+      'config' => array(
+        'param'  => 'key=value',
+        'repeat' => true,
+        'help'   =>
+          'Specify a configuration value for the duration of this command',
+      ),
+    );
+  }
+
+  final public function applyRuntimeConfiguration() {
+    $options = $this->getArgument('config');
+    $manager = $this->getConfigurationManager();
+
+    foreach ($options as $opt) {
+      list($key, $value) = preg_split('/=/', $opt, 2);
+      $manager->setRuntimeConfig($key, $value);
+    }
+  }
+
   final public function parseArguments(array $args) {
     $this->passedArguments = $args;
 
diff --git a/src/workflow/ArcanistHelpWorkflow.php b/src/workflow/ArcanistHelpWorkflow.php
--- a/src/workflow/ArcanistHelpWorkflow.php
+++ b/src/workflow/ArcanistHelpWorkflow.php
@@ -63,6 +63,7 @@
       }
       $optref = array();
       $arguments = $workflow->getArguments();
+      $arguments += $workflow->getGlobalArguments();
 
       $config_arguments = $arc_config->getCustomArgumentsForCommand($command);