That is an interesting and difficult problem. What if it were framed a little differently, though: Suppose there were a federal licensing tax. You'd pay, say, 5% of licensing revenue to the IRS for the first 20 years, 25% for the next 20 years, 60% for the 20 years after that, and so on. Obviously these are made-up numbers, but the idea would be that an increasing fraction of the license revenue would go to government.
I just remembered a variation on a story in which you declare what your property is worth and get taxed on that. The reason not to lower the price is that anyone can buy it from you at that price.
Maybe you can declare the value of your IP and the government taxes you like 2% on it. I don't think this would really work but I'm tossing it out anyway.
