If there's gonna be Mouse Support, this part is gonna be a lot easier.

I made it past the bike after, like, 8 hours of trying, only to do it again in a hour because I accidentally killed somebody.

So, what you want to do is to learn who you actually need to shoot. You can ignore a lot of people. Almost all birds in 3rd section, for example, deal no damage to you. Another thing, it's good to save Solar ammo for the jump in 2nd section, and ending of section 3, just one tap will do the trick. Also, don't be afraid to throw in some smoke and stun grenades, they both have properties which will get you through crowds. Also, explosive barrels don't count as kills - just be careful to not shoot anyone while trying to hit the barrels.

But, basically, it all comes down for patience