I haven't tried this to see if it works.

According to the CGI documentation, you can create an object from an input file.

open my $fh, '<', 'saved-cgi'
    or die "Can't read saved-cgi: $!";
my $cgi = CGI->new( $fh );
[download]

It also says you can create the file it reads with the ->save() method.

So perhaps you can make a new CGI program that does nothing but take a file upload and save the resulting CGI object. Later, load it back in.

Again, I haven't tried this to see that it works, but the documentation seems to imply it would.