Let's assume you go with the embedded JS. Simply output the script based on a condition of your post:

# script head above
if($q->param('f') eq 'done'){
print '<SCRIPT Language=\'JavaScript\'>
history.go(-1)
</SCRIPT>';
}
[download]

In your HTML form simply place a hiden tag:

<INPUT TYPE=hidden NAME=f VALUE=done>
[download]

Similarly, you could place the CGI::redirect object within this conditional block. Forgive me if this is a simplistic response, but it's not very clear what you're after.