Try this:

Code:
{Limit GET}
order deny,allow  
deny from all  
allow from 192.1.2.3  
allow from 192.1.2.4 
allow from 192.1.2.5
Satisfy Any  
{/Limit}
replace the { and } with [ and ] plus change it for the right IP addresses.

Alternatively, you can base it on referrer info
Code:
Options +FollowSymLinks
Options +SymLinksIfOwnerMatch

RewriteEngine on

RewriteCond %{HTTP_REFERER} !^http://www.domain1.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://domain1.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://www.domain2.com/.*$ [NC]
RewriteCond %{HTTP_REFERER} !^http://domain2.com/.*$ [NC]

RewriteRule /*$  http://www.goaway.com [L,R]
repeating the RewriteCond lines for every domain & subdomain you want to allow.

cheers,
Luke