Connecting from Costa Rica

[CorbinMyMan]

I have a user in Costa Rica using a hotel's internet there. When they try to connect to our vpn here it errors out and here in the even log i get the dreaded GRE Packet error. I talked to the MIS department there and they said they have no public IP address and that many people have this problem. They have no server, just a wire that comes into a linksys switch

So my question is how can I allow my vpn to (temporarily) accept private ip clients?

I've looked everywhere! Thanks!