Currently handles ext2/3/4, btrfs and vfat.
         """
-        pseudo = "export PSEUDO_PREFIX=%s/usr;" % native_sysroot
-        pseudo += "export PSEUDO_LOCALSTATEDIR=%s/../pseudo;" % rootfs_dir
-        pseudo += "export PSEUDO_PASSWD=%s;" % rootfs_dir
-        pseudo += "export PSEUDO_NOSYMLINKEXP=1;"
+        p_prefix = os.environ.get("PSEUDO_PREFIX", "%s/usr" % native_sysroot)
+        p_localstatedir = os.environ.get("PSEUDO_LOCALSTATEDIR",
+                                         "%s/../pseudo" % rootfs_dir)
+        p_passwd = os.environ.get("PSEUDO_PASSWD", rootfs_dir)
+        p_nosymlinkexp = os.environ.get("PSEUDO_NOSYMLINKEXP", "1")
+        pseudo = "export PSEUDO_PREFIX=%s;" % p_prefix
+        pseudo += "export PSEUDO_LOCALSTATEDIR=%s;" % p_localstatedir
+        pseudo += "export PSEUDO_PASSWD=%s;" % p_passwd
+        pseudo += "export PSEUDO_NOSYMLINKEXP=%s;" % p_nosymlinkexp
         pseudo += "%s/usr/bin/pseudo " % native_sysroot
 
         if self.fstype.startswith("ext"):