I was having similar problem with to conversion to json on machine where modules cannot be installed. Here is what I end up with (some pieces copied from JSON::PP):

sub to_json {
    my ($ref) = @_;

    if(ref($ref) eq "HASH") {
        return "{".join(",",map { "\"$_\":".to_json($ref->{$_}) } sort
+ keys %$ref)."}";
    }
    elsif(ref($ref) eq "ARRAY") {
        return "[".join(",",map { to_json($_) } @$ref)."]";
    }
    else {
        return "null" if ! defined $ref;
        return $ref   if int($ref) eq $ref;
        my %esc = (
            "\n" => '\n',
            "\r" => '\r',
            "\t" => '\t',
            "\f" => '\f',
            "\b" => '\b',
            "\"" => '\"',
            "\\" => '\\\\',
            "\'" => '\\\'',
        );
        $ref =~ s/([\x22\x5c\n\r\t\f\b])/$esc{$1}/g;
        $ref =~ s/([\x00-\x08\x0b\x0e-\x1f])/'\\u00' . unpack('H2', $1
+)/eg;
        return "\"$ref\"";
    }
}
[download]

Just call it with reference

print to_json({ this => 'that', other => 'whatever' });
[download]

-- hope it helps, Roman