How can I access the internet in a way that proves my physical location?

How can I access the internet in a way that proves my physical location?

Perhaps the opposite of an information security question:

1. Consider a hypothetical where my associate and I have been accused of being the same person abusing multiple accounts on an online forum.
2. Administrators have the power to look up the IP addresses of users.
3. My associate and I are on different continents.

With the internet access options available to the average individual in CONUS and SE Asia (mobile, coffee bar, public library, etc.), and without revealing any personal information other than our IPs, how can my friend and I simultaneously access the internet to prove to someone with a modicum of investigative power that we are, within a high degree of certainty, not using proxies/VPNs/etc., and are separate people at separate locations?

Put another way: there are many methods for disguising your true location when accessing the internet. How can I access the internet in a way that greatly narrows down the number of places I could be, preferably to one?