[filmgeek]

What you'd have to do is run a service like DynDNS.com on your mac. (go to their site to read about it.)

What it does, is keep track of your DYNAMIC DNS (which is likely what you have) by running a program on your mac (@home). Now you can 'find' your mac (via a name, like mjstarks.dyndns.com)

That routes your request to your mac. Then you use 'port forwarding' on your home router, to forward the ports that OmniFocus needs ONLY to your Mac.

So the connection would be like this:
mjstarks.dyndns.com....automatically reroutes your request to your home network/router. Since the data comes in on port 80 (again, this is an assumption, I haven't run the web service), your router in turn pushes the data to your mac.

So, you need to configure three things:
The DynDNS Service
The client for DynDNS on your mac
The router to re-route incoming traffic to your mac (port forwarding)
The OF Software (as it has to be running)

Does that help?