Reply To: Force line break when resizing text box.

You could use a GREP search to add a discretionary line break after every single character.
find: . (a single full stop/period) = any letter or number
replace: $0~k (dollar zero tilde k) = “found text” plus discretionary line break

Works for me with Courier (a monospaced font).

How much is the text content going to change? You might need to re-run the search each time new content is added, as it won’t automatically add the breaks.