Unfortunately not, when you are behind a firewall or router with closed ports, you're stuck.
Also, as to what Arriok wrote, there are many fake servers out there that will tell you that a port is not reachable where in reality it is. You should try to add one real server, the DonkeyServer no2 comes to mind, the real one on 62.241.53.16:4242 (avoid the fake one !!!) and see what respons you get from this one. Delete all other servers, install a ipfilter.dat and you will most likely get a high ID from there on.