getting _POST value of fb:request-form FBML - PHP

Question

Hi there

I am using this following code trying to build an app that simulates sending gift to other users,

<fb:request-form
    action="sendgift"
    method="post"
    type="gifts"
    invite="false"
    content='Enter the name of your friends whom you will send GIFT to <fb:req-choice url="http://apps.facebook.com/appname" label="Confirm" />'
    >
    <input type="hidden" name='gifts_id' value="1"/>
    <fb:multi-friend-selector
    actiontext="Select your friend"
    email_invite="false"
    />
</fb:request-form>

The friend selector shown normally on Fb canvas. But what if I want to grab and do different action in the background between whether user click "Send GIFT Request/Invitation" and "Skip/Cancel" (other bypass values). How can I catch the _POST value?

Also can I include (like in the code above ) inside fb:request-form ?

Thanks