Alternatively, if you only need to debug what the script is doing with the data and not how it is getting the data, you can create a command line flag that tells the script to get the params from a file in whatever format you want to define. If the flag is set just populate the params from the file instead of CGI or whatever you are using.

EDIT: You can already do this with a file and 'use CGI "-debug"' if your file has lines like param1=value1. script.pl < param_file.txt