How to set nodes to be excluded from a block view based in the url of current node?
What you could do if you could use either Views Filters and use the view Filter options to set which URL's to exclude based on tokens.

You could also maybe use Views Rule to try and do something similar.

I think the Views Filters may be an easier option. But if you want to do your suggestion (add a field to the node) then what you can do is pretty much exactly what you said, you would add a filter to the view based upon the available tokens and field data.