Envelope B on the Bridge: 
After knocking out the thug at the start of the level there should be a glowing item on the left when you start. Climb the ladder and jump/glide around the crate onto the other crate. Then, glide onto the platform with the letter.

Envelope E in the Gasworks:
You will reach a room with two levels, each floor with two goons on them. After taking out the goons, look around on the lower floor until you see a sewer pipe with boxes in the sewage. Glide down and land on the first box. Jump over the next few boxes and pick up the envelope with an "E" on it. Finish the game and the "Infinite Health" cheat will be unlocked.

Listings B