openssl_encrypt with a IV of 0xFFFFFFFFFFFFFFFF with encryption mode bf-cbc

I'm using a third party software, that creates key in blowfish in encryption mode CBC and an IV of 0xFFFFFFFFFFFFFFFF. How can I pass an IV like this to openssl_encrypt? The encoding of the source string is windows 1252.

Im using PHP 7.3 with UTF-8.

This are my current attempts:

$data = utf8_decode('12345678');

// if(strlen($data) % 8)
//   $data = str_pad($data, strlen($data) + 8 - strlen($data) % 8, "\0");

$opts = OPENSSL_ZERO_PADDING;

if(defined('OPENSSL_DONT_ZERO_PAD_KEY'))
  $opts = $opts | OPENSSL_DONT_ZERO_PAD_KEY;

echo openssl_encrypt($data, 'bf-cbc', utf8_decode('my-secret-key'), $opts, hex2bin('FFFFFFFFFFFFFFFF')) . '<br />';

$opts = OPENSSL_RAW_DATA | OPENSSL_ZERO_PADDING;

echo base64_encode(utf8_decode(openssl_encrypt($data, 'bf-cbc', utf8_decode('my-secret-key'), $opts, hex2bin('FFFFFFFFFFFFFFFF')))) . '<br />';

The result always differ. The other end is using "Delphi Encryption Compendium Part I-III". I cannot change the way the other software creates the encrypted data. The sourcecode of the version the Delphi software uses can be found here: https://github.com/winkelsdorf/DelphiEncryptionCompendium/releases/tag/1

The Delphi function looks like:

function BlowfishEncryptStr(const InStr, Password: string;
  var OutStr: string; Format: Integer = -1): Boolean;
var
  Cipher: TCipher_Blowfish;

begin
  Cipher := TCipher_Blowfish.Create(Password, nil);

  try
    try
      Cipher.Mode := cmCBC;
      OutStr := Cipher.CodeString(InStr, paEncode, Format);
      Result := True;
    except
      Result := False;
    end;
  finally
    FreeAndNil(Cipher);
  end;
end;

The function is called with this parameters:

BlowfishEncryptStr('12345678', 'my-secret-key');

I tried the IV of 0xFFFFFFFFFFFFFFFF because it seems so, that this is the default of the Delphi Encryption Compendium in this case. I've tried to pass 0x0000000000000000 also.