With Apache's mod_rewrite you can do something like:
RewriteCond %{HTTP_HOST} ^(subsys)\.example\.com
RewriteRule /index.cfm/(.*) /index.cfm/%1:$1
To make it work with multiple subdomains/subsystems, use a pipe-delimited list inside the parentheses:
RewriteCond %{HTTP_HOST} ^(sub1|sub2|sub3)\.example\.com
To make it work for any non-www subdomain, for any domain, use a condition such as:
RewriteCond %{HTTP_HOST} ^((?!www\.)\w+)\.
For IIS6, you would probably need third-party software, such as Helicon Tech's ISAPI Rewrite, which supports mod_rewrite syntax.