I can't think of a way this is possible.
If you only wish to do this for one canvas you could add additional update rules in between to log where people are in the flow directly in a contact field.
Maybe someone else has some ides...
Off of the top of my head, aside from any sort of API work - what if you made shared lists for each "junction / branch"? If they made it into Country A, add to Shared List for "A". Once they exit that particular junction point, remove them from the shared list.
The report itself would run off of the OBIEE contact lists object where you'd use the contact list name and total contacts measurement. You can then apply a filter onto it afterwards to only focus on the specific shared lists for the designated junctions / branches.
Let me know if this would work and I'll be more than glad to show you a sample report if you have the time!
Hong Tai Lee