Can I disable the button part of a XUL toolbarbutton, but not the menu?

Question

I have a toolbarbutton and in certain cases it needs to be disabled. However, I want the menupopup child to still be enabled. Is this possible? If not, any suggestions on how to achieve similar functionality?

I don't want to use two separate buttons for two reasons:

1. I like the look of the entire button being outlined when I hover over the menupopup.
2. There is way too much space between the buttons, even when I set the width on the menu button to be as low as feasible.

Thanks in advance. Here's some sample code for what I am currently doing:

<toolbarpalette id="BrowserToolbarPalette">
    <toolbaritem>
        <toolbarbutton image="&the_img.path;" disabled="true">
            <menupopup>
                <menuitem label="Test label"/>
            </menupopup>
        </toolbarbutton>
    </toolbaritem>
</toolbarpalette>