in reply to
I want to run a script from another script, use the same version of perl, and reroute IO to a terminal-like textbox
This is more a suggestion how you could reach your goal some other way
You could extract the code of the command line scripts to one or more library modules. Then change the scripts to use the library modules. The scripts would just interpret the command line parameters and feed them to the library function.
Now your perl/tk program could use the library functions as well and would neither need to transfer the hash to the scripts nor fight with STDOUT and STDIN.