Becs your friend would be better off cycling to the next station up which is called Hayes as from here you can not only catch Great Western trains, but you can catch the Heathrow Express to Ealing Broadway. You have a higher sucess rate with the express than gw. You will find that from West Drayton carrige capacity is maxed out, but thins slightly at Hayes as people get off here to catch buses and trains to Heathrow.
It's a pretty maxed out route and having experience of this line makes me believe your friend will have big issues and challenges with such a large wheeled bike, even a brompton is on this route.
I would personally only take a bike on this route if catching trains after 9:30am its simply to manic imho.
A far better option for your friend imho would be to buy a cyclecross style bike and ride the length of the Grand union canal towpath which goes from West Drayton to Ealing, it's a pleasurable ride and saves time when compared to waiting for a train which stops for five minutes at each station. Also saves money from train fair.