Speaking as site manager for two of the RAeS' sub-committees, Hamilton Place can't consistently keep a normal website going properly - streaming the couple of lectures going on somewhere in the society each day onto the web would certainly fall into the "too difficult" camp. Arguably this is a shame - whilst a few of these lectures are dull, it's very few.
The high profile "political" lectures often get reproduced in the magazine, but they are rarely the most interesting ones. I'm afraid that turning up at a branch or HQ is the way ahead.
Good news however for those not UK based is that there are active branches in Seatle, Singapore, Hong Kong, Toulouse, UAE, Malaysia, Xiamen, Cyprus... - and for that matter nothing to stop other expat aerospace professionals from starting yet another. I was party to setting up a new branch a couple of years ago (albeit in the UK) and we had all the help we needed in that from HQ.
G