I've reworked the code again, now making it a bit more clever on the mapping %ENV to HTTP::Headers: (comments welcome)

# build a HTTP::Request Object from what CGI.pm provides us with
# see http://www.perlmonks.org/?node_id=854073
sub request_from_cgi {
        my $self = shift;
        my $q = $self->query;
        my $uri = $q->url;
        my $method = uc $q->request_method;

        my %env_to_httpheader = (
                # hash of ENV keys which do not follow the HTTP_* nami
+ng convention
                'HTTP_TE'               => 'Accept-Encoding',
                'CONTENT_LENGTH'        => 'Content-Length',
                # from here on blurry from memory: (and probably more 
+to include as well..), now commented out, see why below:
                # 'CONTENT_ENCODING'    => 'Content-Encoding',        
+  # I think there is only Accept-Encoding on requests
                # 'CONTENT_TYPE'        => 'Content-Type',      # I th
+ink the content-type equivalent on the req side is Accept
        );

        my $headers;
        foreach my $key (keys %ENV) {
                if($key =~ /^HTTP_(.*)$/ && !exists($env_to_httpheader
+{$key})){
                        push(@{ $headers }, lc($1));
                        push(@{ $headers }, $ENV{$key});
                }elsif(exists($env_to_httpheader{$key})){
                        push(@{ $headers }, $env_to_httpheader{$key});
                        push(@{ $headers }, $ENV{$key});
                }
        }

        my $content = undef;
        if($method eq 'POST'){
                $content = $q->param('POSTDATA');
        }elsif($method eq 'PUT'){
                $content = $q->param('PUTDATA');
        }

        if(!defined $content){
                my $len = $ENV{CONTENT_LENGTH} || 0;
                read STDIN, $content, $len;
        }

        return HTTP::Request->new( $method,$uri,$headers,$content);
}
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Update: The PUTDATA param being available might depend on your version of CGI.pm, or use a recent CGI::Simple, which worked for me.