You'll have to edit this, but here's a jist:
popupInviteFriends : function (e) {
if (e) { e.preventDefault(); }
var fbml = '<fb:request-form \
action="." \
method="GET" \
invite="true" \
type="TWO" \
content="This is an invitation from ' + TWOFace.BRAND + '. \
<fb:req-choice url=\'' + TWOFace.INVITE_DIALOG.postBack + '\' \
label=\'Join ' + TWOFace.BRAND + '\' />"> \
<fb:multi-friend-selector \
showborder="false" \
rows="4" \
actiontext="Invite your friends to use ' + TWOFace.BRAND + '"> \
</fb:multi-friend-selector> \
</fb:request-form';
var container = document.createElement('div');
container.innerHTML = fbml;
var inviteIFrame = new FB.UI.PopupDialog(TWOFace.INVITE_DIALOG.title, container);
inviteIFrame.setContentWidth(590);
inviteIFrame.setContentHeight(400);
inviteIFrame.show();
},