What you can do is create hidden field in dialog and retrieve in jsp as
String hiddenValue = properties.get("./hiddenfield", "some default value"));
Node node = currentPage.getContentResource("jcr:content").adaptTo(Node.class);
node.setProperty("hiddenPropName", hiddenValue);
Session session = node.getSession();
session.save();
Above is the sample code you can use, but I suggest you to create a jstl method in your tag library and perform the above logic in a class method.
In jsp you just need to call the taglib method with hiddenValue and currentPage