Agreed, but I'm not sure those are two separate things. How do you force someone to charge more for something? And, presumably, not keep the difference?

They are conceptually two separate things. You can eliminate externalities by making primary productive markets for-use instead of for-profit. Instead of forcing people to do this, you offer incentives (such as much lower cost of housing, much lower cost of running their business, etc) to use software that automates this for them, with the end result being that anybody can see all the inputs to production back to the raw materials themselves for each given product before purchasing it.

I have some great ideas on how to accomplish this all via voluntary participation. Obivously, it would take some time, though.