Here is something I find by browsing the forum, next time you are negotiating peace with an enemy, add in an AI technology, then click option 1 (Will this be acceptable...). Invariably AI will refuse, then you click on option 2 ("let's bury the hatchet, what will make this offer acceptable...). A popup window will come up saying that option is not allowed in peace negotiation, click "OK" to that and go back to the main window and accept the offer. The caveat to this strategy is that more wars and peace negotiations you have--the more free techs you can get. Enjoy your new free technologies. 
Mutax2003

Mutax2003