It is strictly impossible, there is no way. "Port forwarding" means "open his computer, making it accessible to other players." Players come to play in your computer, but they need an opening.
Now, if you need help about forward your port, we can help you. Sometimes, it takes 5 minutes, sometimes, it is much harder.
There is a way, But it goes slower. First get logmein Hamchi from here http://logmein.com, then get your friends to join your network they will need it to, Host a server then tell them to join with your Hamchi ip, and you will be hosting. It will lag a little for them due to restricted speed limt.
On-topic, there isn't any possible way than to port forward. And I still think that joining is more fun than actually hosting, since you're waiting 10 minutes before somebody even joins.
Be the host has also benefits.
1) No Control Lags
2) You can choose which game mode, which level ... you can choose the level for your players, actually.
3) The joy to benefit to your players your server
4) You can customize it, for example putting wads like Tyrcity ... for example.
Returning to the subject, sonic fan2000 ... you can put a cross on your project. Unless if you manage to convince your parents, there is no strategy to host differently.
If the reason you now need to forward your port is due to a wireless router, then just plug the cable from your ISP box directly into your computer. Then put it back in the router when your done. Of course this will render the router useless while your hosting, so it's not a great solution.
This only works if the computer is a laptop and/or close to the router. It will absolutely fail if this is not the case. Why do you think people buy wireless routers? =P
Also, even if this works, it is even more "insecure" than forwarding one port - because in this case all ports are "forwarded", not only the SRB2 port.
In the old days of straight connection of a MODEM to a computer's serial port, the computer was directly behind the IP address, so if someone wanted to connect to say, 45.127.33.240 they are guaranteed to get ONE computer behind it.
Nowadays most MODEMs are built into wireless router/switches. This requires a technology called NAT to allow connections between ONE computer and the outside world. It doesn't allow some random computer to connect to it's IP address and get ONE computer behind it. Port forwarding sets which ONE computer will be seen if a computer tries to connect on that port.