If you just add on an extra class each semester and do summer school, you can do it. Wait, what?
In theory, IN THEORY, you could remove all of your elective time every year, start your PGY3 and PGY4 responsibilities early off-cycle, and finish several months early having completed all of your residency requirements. Never seen that happen. Not sure why anyone would want to do that, or why anyone would want to do the horrendous amount of work to facilitate you doing that.
What you could do is convince all of your PGY4 classmates to let you stack up your year, such that you'd have a few extra months in a row of elective time at the end of PGY4, provided that you go to a very frontloaded program that fulfilled all of your other requirements earlier on. I've seen that happen for a couple of people with R25 projects or those who wanted to start their K08/K23 a bit early.
Are you thinking that there is some sort of analogue to early IM residency completion for those pursuing fellowships? Nope.
It's the only training you're going to get, and you'll still feel unprepared at the end. Savor it. Trying to rush it seems like a bad sign.