In the good old OS/2 days it was easy to rem out the serial or parallel driver from config.sys, reboot, and delete the file (now no longer a reserved name).
The device drivers are supposed to register their reserved entry points with the file system driver as they load -- if they don't load, there should be no reservation. I would try to do something similar... try and get the serial driver not to load (it may be difficult in these days of slug and slay).
Giovanni