Yes you can. Use the HBox#setHgrow();. This javadoc page also has an example how to use it in "Optional Layout Constraints" section. Following is taken from javadoc.
For example, if an hbox needs the TextField to be allocated all extra space:
HBox hbox = new HBox();
TextField field = new TextField();
HBox.setHgrow(field, Priority.ALWAYS);
hbox.getChildren().addAll(new Label("Search:"), field, new Button("Go"));
Briefly speaking, set Priority.ALWAYS
for the button (or any control) just before the "logout-button" in a HBox
. More advanced example is here: Using Built-In Layout Panes : Example 1-4