allowing hostname problem

Hi,

I've got my admincp previously locked via a static ip address. I've since moved and now sadly use a dynamic ip address. I've setup a dynanic dns for it to be linked too but because the server does a lookup on the ip i'm sending from it shows my isp hostname rather than the one already set from dyndns.

Current code

Code:

Options +FollowSymLinks
RewriteEngine on

#Administrator IP / Hostname ONLY
#RewriteCond %{REMOTE_ADDR} !^xx.xx\.xx\.xx$
#RewriteCond %{REMOTE_HOST} !^*\.bb\.broadband\.com
#RewriteCond %{REMOTE_HOST} !^*\.mental\.hostname\.net
RewriteRule .* http://forum.xxx.com/ [R=302,L]

AuthUserFile "/home/xxx/.htpasswds/public_html/forum/xxx/passwd"
AuthType Basic
AuthName "Special Persons's ONLY"
require valid-user

If I allow mental.hostname then it will not work given a traceroute would give my isp provided hostname but if I allow my actual broadband providers hostname it works (obviously). Anyway in which to go around this to only allow the mental.hostname address? Maybe a reverse lookup of some sort.

Thanks.