Jen previously added a great tip to scroll latest activity:

/* Scroll Bar for Latest Activity */
.xg_widget_main .xg_module_activity .xg_module_body {height: 500px;overflow : auto;position:relative;}

But, you may want to keep the 'quick add' options on top of the module while you scroll...
So add:

#xg_network_activity .module-feed {height: 500px;overflow : auto;position:relative;}

You'll also need to adjust Jen's original code to remove that scroll bar and amend the overall height (you'll need to play around with this to get it right):

.xg_widget_main .xg_module_activity .xg_module_body {height: 600px;}

Note that when logged out the Quick Add options dont appear so you will want to check the heights when logged in or out.