Here is one idea you could try.
What I have done for my phpmyadmin to restrict access:
In /etc/httpd/conf.d/phpMyAdmin.conf file:
Code:
<Directory /usr/share/phpMyAdmin/>
AddDefaultCharset UTF-8
<IfModule mod_authz_core.c>
# Apache 2.4
Require local
</IfModule>
<IfModule !mod_authz_core.c>
# Apache 2.2
Order Deny,Allow
Deny from All
Allow from 127.0.0.1 192.168.1.101
Allow from ::1
</IfModule>
</Directory>
Now, phpmyadmin is available from only the server itself (127.0.0.1) and that specific IP (192.168.1.101).
Could you try in a similar way, for example, somewhere in apache's httpd.conf (or some equivalent file ?):
<Directory "/var/www/html/your_limesurvey_root_dir/index.php/admin">
....
....
</Directory>
Let us know how it goes.