Hi ladies,
I too started to see this pattern of habitual waking at around 4 months, it was quite easy to identify once I had read the book because ds was waking at exactly the same time each night, give or take about 30 minutes either way!
I was a little scared to try the wake to sleep initially, so instead I took a less radical approach and simply went to him and settled him without the feed which I had been giving. He protested hotly the first night, but I stayed with him and pat/shh'd to settle. The second night, same thing but less painful to settle. By the end of the week, he wasn't waking anymore.
I think if you can identify it as habitual, it is relatively painless to break the habit. Just stay strong!