Mousemonkey :
http://www.tomshardware.co.uk/forum/id-2023880/choose-answer.html
Thanks for the link. A funny thing happened during that period. I curiously used that feature in a thread where my answer was already chosen as BA and I did undo that immediately, but that removed the BA of that thread totally and hence I lost my newfound power in the process. Nevermind, I'm not craving to have that ability but it is a nice feature since I've seen several people just silently disappear after getting what they want even without a word of courtesy.