diff --git a/scripts/install-multi-user.sh b/scripts/install-multi-user.sh
index 74cc6a5b0..ab41e0242 100644
--- a/scripts/install-multi-user.sh
+++ b/scripts/install-multi-user.sh
@@ -29,6 +29,7 @@ readonly NIX_FIRST_BUILD_UID="30001"
 # Please don't change this. We don't support it, because the
 # default shell profile that comes with Nix doesn't support it.
 readonly NIX_ROOT="/nix"
+readonly NIX_EXTRA_CONF=${NIX_EXTRA_CONF:-}
 
 readonly PROFILE_TARGETS=("/etc/bashrc" "/etc/profile.d/nix.sh" "/etc/zshrc")
 readonly PROFILE_BACKUP_SUFFIX=".backup-before-nix"
@@ -452,9 +453,11 @@ create_directories() {
 }
 
 place_channel_configuration() {
-    echo "https://nixos.org/channels/nixpkgs-unstable nixpkgs" > "$SCRATCH/.nix-channels"
-    _sudo "to set up the default system channel (part 1)" \
-          install -m 0664 "$SCRATCH/.nix-channels" "$ROOT_HOME/.nix-channels"
+    if [ -z "$NIX_INSTALLER_NO_CHANNEL_ADD" ]; then
+        echo "https://nixos.org/channels/nixpkgs-unstable nixpkgs" > "$SCRATCH/.nix-channels"
+        _sudo "to set up the default system channel (part 1)" \
+            install -m 0664 "$SCRATCH/.nix-channels" "$ROOT_HOME/.nix-channels"
+    fi
 }
 
 welcome_to_nix() {
@@ -636,13 +639,14 @@ setup_default_profile() {
         export NIX_SSL_CERT_FILE=/nix/var/nix/profiles/default/etc/ssl/certs/ca-bundle.crt
     fi
 
-    # Have to explicitly pass NIX_SSL_CERT_FILE as part of the sudo call,
-    # otherwise it will be lost in environments where sudo doesn't pass
-    # all the environment variables by default.
-    _sudo "to update the default channel in the default profile" \
-          HOME="$ROOT_HOME" NIX_SSL_CERT_FILE="$NIX_SSL_CERT_FILE" "$NIX_INSTALLED_NIX/bin/nix-channel" --update nixpkgs \
-          || channel_update_failed=1
-
+    if [ -z "$NIX_INSTALLER_NO_CHANNEL_ADD" ]; then
+        # Have to explicitly pass NIX_SSL_CERT_FILE as part of the sudo call,
+        # otherwise it will be lost in environments where sudo doesn't pass
+        # all the environment variables by default.
+        _sudo "to update the default channel in the default profile" \
+            HOME="$ROOT_HOME" NIX_SSL_CERT_FILE="$NIX_SSL_CERT_FILE" "$NIX_INSTALLED_NIX/bin/nix-channel" --update nixpkgs \
+            || channel_update_failed=1
+    fi
 }
 
 
diff --git a/scripts/install-nix-from-closure.sh b/scripts/install-nix-from-closure.sh
index 635aaa16d..826ca8b8c 100644
--- a/scripts/install-nix-from-closure.sh
+++ b/scripts/install-nix-from-closure.sh
@@ -41,7 +41,6 @@ fi
 
 INSTALL_MODE=no-daemon
 CREATE_DARWIN_VOLUME=0
-NIX_EXTRA_CONF=
 # handle the command line flags
 while [ $# -gt 0 ]; do
     case $1 in
@@ -50,20 +49,20 @@ while [ $# -gt 0 ]; do
         --no-daemon)
             INSTALL_MODE=no-daemon;;
         --no-channel-add)
-            NIX_INSTALLER_NO_CHANNEL_ADD=1;;
+            export NIX_INSTALLER_NO_CHANNEL_ADD=1;;
         --daemon-user-count)
-            NIX_USER_COUNT=$2
+            export NIX_USER_COUNT=$2
             shift;;
         --no-modify-profile)
             NIX_INSTALLER_NO_MODIFY_PROFILE=1;;
         --darwin-use-unencrypted-nix-store-volume)
             CREATE_DARWIN_VOLUME=1;;
         --nix-extra-conf-file)
-            NIX_EXTRA_CONF=$(cat $2)
+            export NIX_EXTRA_CONF="$(cat $2)"
             shift;;
         *)
             (
-                echo "Nix Installer [--daemon|--no-daemon] [--no-channel-add] [--no-modify-profile]"
+                echo "Nix Installer [--daemon|--no-daemon] [--daemon-user-count INT] [--no-channel-add] [--no-modify-profile] [--darwin-use-unencrypted-nix-store-volume] [--nix-extra-conf-file FILE]"
 
                 echo "Choose installation method."
                 echo ""
@@ -82,6 +81,10 @@ while [ $# -gt 0 ]; do
                 echo " --no-modify-profile: Skip channel installation. When not provided nixpkgs-unstable"
                 echo "                      is installed by default."
                 echo ""
+                echo " --daemon-user-count: Number of build users to create. Defaults to 32."
+                echo ""
+                echo " --nix-extra-conf-file: Path to nix.conf to prepend when installing /etc/nix.conf"
+                echo ""
             ) >&2
 
             # darwin and Catalina+