procedure StreamToBlob(ADataSet: TDataSet; AField: TField; AStream: TStream);
var
  BlobStream: TStream;
begin
  BlobStream := ADataSet.CreateBlobStream(AField, bmWrite);
  try
    BlobStream.Position := 0;
    BlobStream.CopyFrom(AStream, 0);
  finally
    BlobStream.Free;
  end;
end;

procedure TForm14.Button1Click(Sender: TObject);
var
  MemoryStream: TMemoryStream;
begin
  MemoryStream := TMemoryStream.Create;
  try
    // load something into the MemoryStream...
    StreamToBlob(ABSQuery1, ABSQuery1.FieldByName('YOUR_BLOB_FIELD_NAME'), MemoryStream);
  finally
    MemoryStream.Free;
  end;
end;