How to do localization in a BXML Prompt

[Brendan cheng]

Hi,
in my bxml file, I use a Prompt
    <bxml:define>
        <Prompt bxml:id="confirmCloseTabPrompt" title="%ConfirmCloseTab"
            message="%Reallyclosethistab"
            options="['Cancel', 'OK']" selectedOptionIndex="1"/>
    </bxml:define>
where all other string I can use % for substitution, except the Cancel and OK.
Is there a way of doing it?
Brendan