As far as I know there is no way of doing this as of yet, not unless its hidden by some keyboard shortcut that I do not know about. If you go to the help menu (Inside the Designer application) and click give feedback, it will take you to a how can we improve Substance Designer page. Look on their to see if anyone has requested this as a feature and up vote it, the more votes the more attention, if nobody has, you can create one yourself.
Hope this helps.
Regards
Joel B.
