Augmented reality games or not, if real value were ever associated with proof-of-location then I'd imagine people would attempt to develop and sell location remoting services. For the system to work the value of the proof has to be less than the cost of "spoofing" a location.
In a somewhat related example, I knew of somebody who needed to trade as a non-US person on a well known Bitcoin exchange. The cost of setting up a non-US account and a secure computer in a foreign country was well within his budget given the particular circumstances. So he went ahead and did it although it cost him almost $10K. The setup served him well and in spite of AML/KYC checks he was able to trade from a fake country under a someone else's name.
I would think that it would cost a lot less then this to spoof your location.
Wouldn't it be cheaper for your friend to simply go to this location for a month, rent a room, buy a computer and actually be in this location?