EDIT: Posted before, I realized that you'd already found a solutions

Or something similar. Perhaps use an Array rather than different variables in the output TextBox. You'll need to select the Constant Expression option when you select Insert Variable.
1. create array in the Variables Tab of the Page properties.
2. Use an action or script object to fill in the fictional parts of the dialogue. IE
myArray[0] = "hello"
myArray[2] = "What is you name?"
myArray[4] = "How comes?"
Then in the Text Box, add all the array elements for the entire dialogue. IE
myArray[0]
myArray[1]
myArray[2] - etc - etc
On the button, have an action that copies the myInput variable into the correct array element when the user clicks enter - IE element [1] then [3] etc. This could just be a counter incrementing in twos.
This is a rather long winded and involved approached, but anything else probably requires a little more complex scripting

Regards,
Mack