How can we add placeholder text to an input table?

Hello,

I have a spreadsheet that I would like to have text in light grey in some cells but still allow the cell the be populated by the user.  

ie. Have the text "x1" repeat in all columns below so the user knows which column it is even if the header row is not visible.

It is not currently possible to add placeholder text to input tables.  It is possible to pre-populate values inside of the field is via URL parameter or with pre-populate app:

http://prepopulate.jotform.io/

Prepopulating Fields to Your JotForm via URL Parameters

But it would be actual values in the table, not placeholder text.