Dynamic Path-Prepend based on beginning of URL.

I need to be able to path-prepend a dynamic URI based on the beginning of the URL. For example we use:

when HTTP_REQUEST {
if { [HTTP::path] "/" } {
HTTP::redirect "/abc/" }
}

Instead of hard coding /abc/ in there, is there a way to have it pull from the URL? For example the URLs would be http://abc.worldwide.taco.com and http://def.worldwide.taco.com. These would also be the URI/context roots for the applications(abc and def).

Thank you