In version 5 (which is what I use and currently don't intend to upgrade) you have to write a script that locates the duplicated fields and then sets their value.
Essentially, you obtain the number of times it is repeated from the underlying form object and use that to do a loop, using the loop index to reference each occurance. You can also go through the complete collection of objects and when one with the same name is found, you would set its value. The first method is more efficient. In version 5, at least, you do have to recognize when the loop is referencing the source field and not update it or weird things would happen.