Facebook connect - automatic trigger 'request extended permissions' dialog

For certain pages(functionalities) of the site, i need different permissions. I am requesting those permissions only if (and when) u开发者_开发问答ser is accessing those parts of the site.

The normal flow is to display a 'Please allow us to send you emails' link using something like:

<fb:prompt-permission perms="email"">
    Please allow us to send you emails
</fb:prompt-permission>

My question is: how can I automatically trigger this dialog, so that user shouldn't click on the 'Please allow us to send you emails' link?

You can directly call this JavaScript function:

FB.Connect.showPermissionDialog(...)

Thanks