The simplest approach would be to insert a space character into the otherwise empty content controls. There is no need to modify the Placeholder Text.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

The problem with that, though, is that this document is filled out in different stages. The first stage involves filling out around 25 of these content controls which would mean the user would have to put a space in the other 75 content controls. Then, when they have to go back into the form and fill out the next 15-20, they won't see them. A lot of the users are not familiar with content controls so even if they did come across them, they would have no idea that they are supposed to fill them out if there's no placeholder text to tell them to do so.