The first '/' in your ScriptAlias parameter is not a script and therefor invalid for ScriptAlias. Have you tried a UrlToolkit rule yet?
UrlToolkit {
ToolkitID = my_rule
RequestURI exists Return
Match .* /script.cgi
}
This UrlToolkit rule is just a guess. I have no idea what CMS/framework you are using or how your website works.