Resist the temptation to undercut your coworkers. There are several reasons why you should avoid this.
- Your coworkers know your value, and they may already be advocating for you and you just don't know it. If you undercut them, at the least they won't advocate for you, and at the worst they will undercut you.
- Your boss sees them as experts already, and he's unlikely to up and decide they don't know as much as he thinks on your say-so. More likely, he will think less of you.
- You may really not know as much as they do--it just might be that their expertise lies in areas you haven't been exposed to or can't appreciate at this stage in your career.
So, now we know what you shouldn't do, what are some things you should do?
Seek ownership of something. I've had bosses who were unable to imagine that one person could be expert at more than one thing. By the same token, they equally could not imagine that more than one person could be expert at the same thing. You're not going to displace the person who's already in their mental "expert" slot for the thing. So get your own thing, and you will be king of the expert slot for that thing.
Advocate for your coworkers. This earns you goodwill from your coworkers, and may act as a "hint" to them about what you'd like to see them do. An immediate benefit from this is that the "glow" of positive energy your boss has toward them will wear off on you. It's easier for him to see you as an expert in something if your opinion of who is an expert seems to align with his. Keep in mind that the reason he thinks they are expert is likely that they produced significant business value for him. Even if they could have produced even more business value with your vaunted expertise, that doesn't negate that they were the ones who actually produced the business value when it mattered.
Be strategic in trying to reshape his opinion. You can gently and subtly correct his impression of who did what if you're strategic. So, instead of blurting out "I wrote that code, not Tom," maybe something more like "I wish I'd known that code that did this existed before I wrote the code for Project X. I spent half a day writing that." Of course, be very sure that there wasn't any such code before you say that. With any luck, your boss will think back and realize that he can't remember any code that did that before Project X.
Make sure your boss is aware of the things you are doing to improve yourself. Going to a user group meeting? Let your boss know the day before that you're working late so that when you leave early to go to the meeting it won't affect your performance. Connect to him on LinkedIn and make sure you always post a status update when you write a blog post. Speaking at a conference? Make sure you let your boss know about when you ask for the time off to go. If your coworkers are also doing these things, it's important to make sure that you are promoting your own efforts so it's clear you are also concerned with your development. If they're not, it is likely (but not guaranteed) that your boss will realize over time that people who make efforts at self-development develop faster than those who don't (in general).
Ultimately, you may just be stuck with your boss's initial impression of you. My husband is internationally recognized as knowledgeable at what he does, and it was never going to matter at the job he held until about 6 months ago. He ultimately changed jobs, and he's very happy. Ironically, his department was spurred by his departure into at least half-hearted measures to retain the employees they have left.