Default values for blank text items in editor?

I am using some calculated Text items which are often blank (e.g., % chance of rain.) This makes WYSIWYG editing of the layout impossible, because the positions and visual attributes of these text items are invisible. The only workaround I've found is to temporarily replace the formulas with actual strings of visible text. But it's a real pain to switch back and forth, including having to save complex formulas into a separate document so I can copy/paste them back into place before saving my edits.

Is there some option to predefine a string of default text (just like other item attributes such as font, size, etc.) which would automatically be displayed during editing if that item's calculated value is currently blank?

A placeholder frame/outline would be an alternative, but would only help in positioning - you still couldn't see the effects of other visual text attribute settings.