That doesn't really tackle my point regarding that you don't know what your gains are, because you don't know which coins you are exactly selling. If they are all fractional-mined at different values, you are getting profits or losses depending on WHEN they were mined. There is no way to track that information.
It would be pretty easy to write a script, using the blockchain API to iterate all the mining receive transactions during the tax year on the receiving address(es) and to get a historical exchange values from the same API. The databases exist for free of charge, and you most likely have a computer that could run such a script.
Agreed. If there is a demand and especially if people are willing to put up a little BTC for it then I'm sure programs will pop up to pull the exchange rates and help do the needed calculations.