Hello dqattan,
If you do not require high level of precision, you can measure the GCPs with the common GPS device (performing several measurements for each point to minimize the error).
In principle, if you have several reference distances measured in scene you can use them as scale bar instances in PhotoScan (applying correct scale to the model), then adjust the model orientation relatively to the coordinate system axes in the bottom-left corner of the Model view (by eye) and then execute the following line in the Console pane of PhotoScan Pro window to emulate the georeferencing:
PhotoScan.app.document.chunk.transform.matrix = PhotoScan.app.document.chunk.transform.matrix