reapply Ike's pull-request in a new branch. The PR branch got mangled on the rebase by accident.

cms/djangoapps/contentstore/utils.py

@@ -80,10 +80,15 @@ def get_lms_link_for_item(location, preview=False, course_id=None):
         course_id = get_course_id(location)
 
     if settings.LMS_BASE is not None:
-        lms_link = "//{preview}{lms_base}/courses/{course_id}/jump_to/{location}".format(
-            preview='preview.' if preview else '',
-            lms_base=settings.LMS_BASE,
-            course_id= course_id,
+        if preview:
+            lms_base = settings.MITX_FEATURES.get('PREVIEW_LMS_BASE',
+                'preview.' + settings.LMS_BASE)
+        else:
+            lms_base = settings.LMS_BASE
+     
+        lms_link = "//{lms_base}/courses/{course_id}/jump_to/{location}".format(
+            lms_base=lms_base,
+            course_id=course_id,
             location=Location(location)
         )
     else:

cms/djangoapps/contentstore/views.py

@@ -317,8 +317,11 @@ def edit_unit(request, location):
             break
         index = index + 1
 
-    preview_lms_link = '//{preview}{lms_base}/courses/{org}/{course}/{course_name}/courseware/{section}/{subsection}/{index}'.format(
-            preview='preview.',
+    preview_lms_base = settings.MITX_FEATURES.get('PREVIEW_LMS_BASE',
+        'preview.' + settings.LMS_BASE)
+
+    preview_lms_link = '//{preview_lms_base}/courses/{org}/{course}/{course_name}/courseware/{section}/{subsection}/{index}'.format(
+            preview_lms_base=preview_lms_base,
             lms_base=settings.LMS_BASE,
             org=course.location.org,
             course=course.location.course,