Hope you don't mind a guy popping in, but I wonder if you could just not mention them, period, and just tell people you're trans when you're ready. How many people are going to ask you what's going on with your chest? I imagine most people would feel rude or weird about asking and making a scene. Especially when, while they will be noticeable, the growth is still fairly gradual and you'll probably start off with A cups for a while.
I say this because I am clearly male at this point, and I've been showing up to work in a sports bra and thin t-shirt because it's too hot and my job is too active - I'd probably get a heat stroke if I tried to hide my chest! I'm sure some people have thought "geez, why does that guy have such big boobs?" especially when I had to run today and they jiggled. But no one has asked, and these are the type of people who have zero education on trans issues, so if they thought something was off about my maleness they'd call it like they see it.