Before starting up I Now Know Why You Cry, change your character to Tweed so you can use the C4 that you will find in a few areas during and after your confrontation with Nemesis. There are about 4 C4 packs that you can find throughout the area, but you'll only need 1 for the door, and do note that Nemesis' rocket launcher will blow up the two gates you need to get through if you manage to get him to shoot the doors. Two easy C4 packs to find are the one by the crashed helicopter in the park, and the other is in the Foundry building at the base of a staircase to a USS soldier in a fortified position (this one is just after the door you need to C4). Upon entering the Foundry from the sewers, head to the right and you'll see a large cell door with a room full of ammo and grenades behind it. Use your C4 on it to destroy the door and let yourself in.