Domain name redirects ?

You could always just create a php file that will redirect to the post you want!

[PHP]<?
Header( "HTTP/1.1 301 Moved Permanently" );

Header( "Location: http://domainname.blogspot.com/firstpost&quot; );
?> [/PHP]

You'd name it your post title and place it in your /web folder on reg365.

eg. if you called it "firstPost.php"
then with it being in your /web folder you would access it through
www.domainname.com/firstpost.php
and it would redirect it to what ever address you put in the php file

Not the most elegant solution, as you'd have to create a new file for every new post you'd make, but you can try it if you want!

Edit...
Threw a working example up so you can see how it works
http://stephenflynn.ie/boards.php
it'll redirect you to the boards website!