Another option might be GRE, unless
a) I don't understand GRE properly
b) my ISP filters that
c) there's no way to bypass for a gateway route the generic restriction that a GRE routing entry can't be more generic than the link it uses to be transported over (which of course in the case of a gateway rout, it would be).
Personally, I don't care WHAT I use. I can put a pfSense (or Vyatta, if it has to be) box on both sides of the link. Anything that's in my budget (i.e. free software and $150 nettop on each end) is an option as long as it can
route the class-C network through some sort of logical tunnel of sorts such that the gateway is logically at the colocation provider, while it's physically here in my home
there's a possibility to have a guest LAN bypass all of that, and via NAT access the internet directly through the ISP without detour of the tunnel
I can have a few additional private-LAN to private-LAN IPSec VPNs to clients and friends' LANs
Ideally, it would also allow
4) policy based routing, such that end-user web traffic, downloads, etc. use NAT and don't do the colocation routing detour
5) VoIP PBX (like FreeSwitch module in pfSense).
My problem is, the current setup works, sort of, but not trouble free, but it works (it hangs itself rather often, needs resetting on a regular basis, the box sometimes gets overloaded etc.).
I'm not in a position though to spend $300-$500 all said and done on hardware and equipment installation charges at the colocation provider, just to figure out that it won't work; the whole operation is only meaningful if it moves me from "sort of works" to "works" ;)
I wish there were someone who could answer a question like that…