Id recommend as phishphreek80 said to set up a box to work as a firewall/ router. look at coyote linux its simple to use and runs on a 486 which can be had for a few quid (my last 486 cost me £3). Then it would just be a matter of iptables.

I really dunno whether this would work, but could you not create a c program, that closes the port, using the winsock standard close port, put this in a loop that continually loops.

just an idea, im sceptical whether that would work

i2c