If you have the authority to connect to that computer over the internet, then you can set that connection up so that splunk shares that authority.
It might be easier or more appropriate to set the other computer up to push the logs to a place that splunk can pull them without breaching security. They could be mirrored out to a google drive, or a number of other solutions. It all depends upon your security posture with regard to each of the boxes, and the sensitivity of the data.
