This is a hard one, if there is a way I'd like to know. But all my attempts thus far have been failures. Port Forwarding won't work, and likely both computers would have to be exposed to the Internet in order for it to work.
I think the answer is probably going to be no. Now, something else I'd be interested in knowing, Dynaverse Servers have to go through the Directory Server in order to connect, and I was told (as of two years ago) that there was no way around that. Are the Directory Servers just that, a place where you can find all the Servers, or does their connection linger well after you select which server you are on? If it doesn't linger, something you could do, and something I may do myself, is set up a private server that can be accessed from different computers on the LAN. Since your LAN addresses are different, there shouldn't be a problem. If this would work, I could set up the Errand of War Server that's been on the back burner for far longer than I wanted it to be. It's on hold because I haven't had the time to test it, but if I could set it up on my LAN, I could dragoon my roommate and a couple of other friends into testing it with me.