Copying a variable state in a delegate literal definition

[Andrej Mitrovic]

So I have this code right here (semi-pseudocode) inside a "MenuBar" widget:

void showMenu(index menuIndex) { }
void appendMenuButton()
{
    static size_t menuIndex;
    // create menu button, and then:
    button.connect!(Signal.MouseClick) = { this.showMenu(menuIndex); };
    menuIndex++;
}

button is a newly constructed widget object, Signal is just an enum.
Inside of my Widget class I have this:

    void delegate()[] clickHandlers;

    @property void connect(Signal signal)(void delegate() dg)
    {
        static if (signal == Signal.MouseClick)
            clickHandlers ~= dg;
        else
            // ...
    }

    void onClicked()
    {
        foreach (handler; clickHandlers)
        {
            handler();
        }
    }

So far so good. This works except for the following quirk:

button.connect!(Signal.MouseClick) = { this.showMenu(menuIndex); };

Inside this lambda menuIndex is accessed through that frame pointer
when the lambda is called. But I actually want a *copy* of menuIndex
at the definition site. Because as I call appendMenuButton() numerous
times, menuIndex is increased, so if I do this:

menu.appendMenuButton();
menu.appendMenuButton();

 { this.showMenu(menuIndex); }; becomes:
 { this.showMenu(2); };

when it is called. I can't use a function literal instead of a
delegate literal because I want to have access to "this.showMenu", but
I want a copy of menuIndex. I've tried this:

{ size_t index = menuIndex; writeln(index); }

However that doesn't copy the state either, it initializes index with
the menuIndex in the frame pointer when the literal is called.

So how can I selectively copy the state of some variables at the site
of the definition of a delegate literal?