diff --git a/functions b/functions
index dbe9d30..8008500 100644
--- a/functions
+++ b/functions
@@ -7,6 +7,7 @@
 # ``GLANCE_HOSTPORT``
 # ``OFFLINE``
 # ``PIP_DOWNLOAD_CACHE``
+# ``PIP_USE_MIRRORS``
 # ``RECLONE``
 # ``TRACK_DEPENDS``
 # ``http_proxy``, ``https_proxy``, ``no_proxy``
@@ -578,7 +579,8 @@
 
 
 # Wrapper for ``pip install`` to set cache and proxy environment variables
-# Uses globals ``OFFLINE``, ``PIP_DOWNLOAD_CACHE``, ``TRACK_DEPENDES``, ``*_proxy`
+# Uses globals ``OFFLINE``, ``PIP_DOWNLOAD_CACHE``, ``PIP_USE_MIRRORS``,
+#   ``TRACK_DEPENDS``, ``*_proxy`
 # pip_install package [package ...]
 function pip_install {
     [[ "$OFFLINE" = "True" || -z "$@" ]] && return
@@ -597,11 +599,14 @@
             CMD_PIP=/usr/bin/pip-python
         fi
     fi
+    if [[ "$PIP_USE_MIRRORS" != "False" ]]; then
+        PIP_MIRROR_OPT="--use-mirrors"
+    fi
     $SUDO_PIP PIP_DOWNLOAD_CACHE=${PIP_DOWNLOAD_CACHE:-/var/cache/pip} \
         HTTP_PROXY=$http_proxy \
         HTTPS_PROXY=$https_proxy \
         NO_PROXY=$no_proxy \
-        $CMD_PIP install --use-mirrors $@
+        $CMD_PIP install $PIP_MIRROR_OPT $@
 }
 
 
diff --git a/tools/xen/install_os_domU.sh b/tools/xen/install_os_domU.sh
index 0bb6ac8..c78c6f2 100755
--- a/tools/xen/install_os_domU.sh
+++ b/tools/xen/install_os_domU.sh
@@ -57,8 +57,8 @@
 fi
 
 # get nova
-nova_zipball=$(echo $NOVA_REPO | sed "s:\.git$::;s:$:/zipball/$NOVA_BRANCH:g")
-wget $nova_zipball -O nova-zipball --no-check-certificate
+NOVA_ZIPBALL_URL=${NOVA_ZIPBALL_URL:-$(echo $NOVA_REPO | sed "s:\.git$::;s:$:/zipball/$NOVA_BRANCH:g")}
+wget $NOVA_ZIPBALL_URL -O nova-zipball --no-check-certificate
 unzip -o nova-zipball  -d ./nova
 
 # install xapi plugins