I have added a feature to automate the keyboard input through a serial port. There are some posts on the forum (like http://vogons.zetafleet.com/viewtopic.php?t=16881&highlight=sendkeys&sid=5707795e7ff9e0b10c3a0986034a5004) where people were looking to automate the program control. I had a similar need, so that is why I wrote it.
There is a project on sourceforge called com0com that loops two virtual serial ports together that I am using in combination with this modification (one end connected to DOSBox, other end connected to the master program that will control the program running in DOSBox).
To use the modification, setup parameters in the configuration file the same as "directserial" but change the type to "directserial_keyboardsim". Refer to sample conf file attached. Then just pass the desired keystrokes through the serial port.