The character you see on screen is either a tiny icon or an @ sign. Most of the time, references to the character are through the pronoun "You", which is gender neutral. The few directly masculine references are in flavor text of the trait descriptions, which are minor. Any added gender-switch would be purely cosmetic, do nothing but flip a few random words in the skill descriptions, and be all-around kinda pointless.
You want to play a doomgal, put a femme name when prompted for one. This achieves exactly as much as a gender option would.