If you decide to go the htaccess method, here's the best way to do it. This will load a new image for all of the fusker sites, not just fusker.lewww. Depending on your server, you may not need the first 2 lines below.
Options +SymLinksIfOwnerMatch
RewriteEngine on
RewriteCond %{HTTP_REFERER} .*.fusker* [NC]
RewriteRule .*\.(gif|jpg|jpeg|bmp)$
http://www.yourdomain.com/hotlink.gif [R,NC]