diff --git a/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php b/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
--- a/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
+++ b/src/applications/diffusion/management/DiffusionRepositoryStorageManagementPanel.php
@@ -190,15 +190,19 @@
           }
         }
 
+        $last_writer = null;
+        $writer_epoch = null;
         if ($write_properties) {
           $writer_phid = idx($write_properties, 'userPHID');
-          $last_writer = $viewer->renderHandle($writer_phid);
+
+          if ($writer_phid) {
+            $last_writer = $viewer->renderHandle($writer_phid);
+          }
 
           $writer_epoch = idx($write_properties, 'epoch');
-          $writer_epoch = phabricator_datetime($writer_epoch, $viewer);
-        } else {
-          $last_writer = null;
-          $writer_epoch = null;
+          if ($writer_epoch) {
+            $writer_epoch = phabricator_datetime($writer_epoch, $viewer);
+          }
         }
 
         $rows[] = array(
diff --git a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
--- a/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
+++ b/src/applications/diffusion/protocol/DiffusionRepositoryClusterEngine.php
@@ -11,6 +11,7 @@
 
   private $repository;
   private $viewer;
+  private $actingAsPHID;
   private $logger;
 
   private $clusterWriteLock;
@@ -44,6 +45,23 @@
     return $this;
   }
 
+  public function setActingAsPHID($acting_as_phid) {
+    $this->actingAsPHID = $acting_as_phid;
+    return $this;
+  }
+
+  public function getActingAsPHID() {
+    return $this->actingAsPHID;
+  }
+
+  private function getEffectiveActingAsPHID() {
+    if ($this->actingAsPHID) {
+      return $this->actingAsPHID;
+    }
+
+    return $this->getViewer()->getPHID();
+  }
+
 
 /* -(  Cluster Synchronization  )-------------------------------------------- */
 
@@ -402,7 +420,7 @@
       $repository_phid,
       $device_phid,
       array(
-        'userPHID' => $viewer->getPHID(),
+        'userPHID' => $this->getEffectiveActingAsPHID(),
         'epoch' => PhabricatorTime::getNow(),
         'devicePHID' => $device_phid,
       ),
@@ -433,8 +451,6 @@
       return;
     }
 
-    $viewer = $this->getViewer();
-
     $device = AlmanacKeys::getLiveDevice();
     $device_phid = $device->getPHID();