Shoutbox

well I think you want to use Universal plug n Play port mapping, I wouldn't quite use hamachi but maybe a porable version (buri) might be plausible
but may be more trouble than it's worth, hamachi connects to the logmein ppl's server then you create a new virtual network then have others join it gives you an ip address for your virtual network.

Soardra has the most common solution but you could try and do something with port mapping (you could also connect outbound of your gateway to the target ip as outbound is eaiser to unblock but my guess is that is not what you want to do)