My situation is the following: I\'ve got a lot of small gizmos ( pretty close to routers, not exactly but anyway that\'s irrelevant) ; they are running a bare-bones MIPS-based L
Have you tried driving the serial port with a kermit script? I would probably forgo trying to insert a more clever proxy on the device and just try and drive the existing interface.
If you really want to get it on the device, you may be able to look at the source to something like screen or kermit to get a sense of how they interact with ttys.
You might want to take a look at reptyr. It will probably need some adaptation to work for your system though