Kinda ugly, and I lifted it from an old post, but this should work:
import readline
readline.set_startup_hook(lambda:
readline.insert_text('supercalifragilisticexpialidocious'))
try:
new_value = raw_input()
finally:
readline.set_startup_hook(None)-- http://mail.python.org/mailman/listinfo/python-list
