Well depending on how old he is, being a lecturer I will assume he is at least in his 20's if not older, why not get him a recorder so he can record his lectures? It is a bit pricey but it is very high end, take a look at the H2 Handy Recorder by ZOOM. It allows for mono and stereo recording. It can be hooked up to a system as a standalone microphone as well. It has a USB interface to trasfer recordings from the H2 directly to your PC for editing or recording to CD. It isn't real expensive but it may be more than you were thinking about paying for a gift. But that is for you to decide.
The cheapest place I found to order one was here https://secure.bhphotovideo.com/c/s ... t=zoh2&N=0&InitialSearch=yes (that is a search result page for zoh2(model number)) I just bought one a little over a month ago. A recorder would allow him to record any lecture and provide it to people who couldn't attend. It would also allow him to listen to his own lecture and take notes about things that could use improvement/clarity.