How do I unregister a Handler in net/http?

I am writing a web server wherein I need to register handlers at runtime. E.g. "/create" would create a new handler for all URLs like "/123/*" and so on. I need a corresponding "/destroy/123" which would unregister the handler for "/123/*".

Here's the code for handling "/create"

package main
import (
    "fmt"
    "net/http"
)

type MyHandler struct {
    id int
}
func (hf *MyHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintln(w, r.URL.Path)
}

// Creates MyHandler instances and registers them as handlers at runtime
type HandlerFactory struct {
    handler_id int
}
func (hf *HandlerFactory) ServeHTTP(w http.ResponseWriter, r *http.Request) {
    hf.handler_id++
    handler := MyHandler{hf.handler_id}
    handle := fmt.Sprintf("/%d/", hf.handler_id)
    http.Handle(handle, &handler)
}

func main() {
    factory := HandlerFactory{0}
    http.Handle("/create", &factory)
    http.ListenAndServe("localhost:8080", nil)
}

I tried implementing my own multiplexer by embedding http.ServeMux but it holds its pattern-to-Handler mapping in a private variable (ServeMux.m)