If anyone came across with same problem, this guide http://www.geocities.jp/arduino_diecimila/bootloader/index_en.html solves it.
And if you got Seeeduino from Seeedstudio like me: bitbang pins X3 of Diecimila called UART on Seeeduino.
Seeeduino's bitbang pins are labled according to config file of AVRDUDE. If you refer to the guide, the mapping is like this:
seeedstudio uart arduino x3
CTS --> 1
DSR --> 2
DCD --> 3
RI --> 4