Not in beta 4, but in beta 5, yes. Just use a php type block there and do a call to a SSI.php function. But as I said, the "recent topics" has already been done for you in that beta. Basically it collects data from the function and output them in a compact way, because just letting the function do the rendering itselfdefault behavouir will make it too big to fit in a block - in width.