You can set $ENV{var} in your process and then call the rest of the scripts with fork+exec.
For example:

Parent (your script):

#!/usr/local/bin/perl
use strict;
use warnings;

$ENV{foo}="bar";

if (fork == 0){ #child
        exec("./foo.pl");
} else{
        print "I'm the parent $ENV{foo}\n";
}
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Child (other scripts):

#!/usr/local/bin/perl

print "I'm the child $ENV{foo}\n";
[download]

This works because environment is propagated to childs (and filehandles and...).

Search for fork+exec for more information.