Universal Plug & Play support is something that has been requested before, hopefully Khaled will implement the idea in an upcoming version of mIRC.
For now, there are a number of ways you can do this.
if you use a software firewall(zonealarm, blackice), allow mIRC to be run 'as a server' and it will work around this.
If you have a router or are using Internet Connection sharing, route a port (or multiple ports) through your router in succession to eachother, TCP mode, to your computer behind the network.
This will give you a maximum of 4 DCC sends at one time.
This will not affect your ability to receive DCCs.