There is a metal hatch on the ground just outside the subway entrance, on the left side. This hatch leads to a network of ducts that you can use to get onto the subway platform while bypassing the main entrance. Avoiding the attention of the NSF personnel on the subway platform will still be something you have to deal with, however.

You can see the location of the hatch at 7:56 in this video.

There is a metal hatch on the ground just outside the subway entrance, on the left side. This hatch leads to a network of ducts that you can use to get onto the subway platform while bypassing the main entrance. Avoiding the attention of the NSF personnel on the subway platform will still be something you have to deal with, however.

You can see the location of the hatch at 7:56 in this video: