For this month you're going to compliment a girl you know about something very feminine. It can be a clothing, her hair, her makeup, her shoes... Something feminine a man would not care about. You must sound really friendly in the way you compliment her. Like a gay friend.
The sexier your friend present, the more friendly you will become. She should see you only as a friend.
Make her say things she would say to a female friend. Have a small girly talk with her.
Do not force things. Let her do the talking if she wants. Listen carefully to her
If you do this right, you will gradually start turning from a regular guy to "seemingly straight" This will slowly change the way she perceived you. You will be regarded more like a "girl".