How to make someone Gay!
You can't. No one can.
People are born with different emotions and feelings. Different social factors such as family, friends and schoolmates help determine if someone is going to act upon those feelings.
So they have a choice, either act upon their emotions or dismiss them. People see such rampant harassment of bisexuality that it is easy for them to try to hide their true feelings.
There are nasty stereotypes of what a bisexual is supposed to be. So, they often feel that they do not fit these crude descriptions and this makes it even easier to dismiss their true emotions.
For emotional well being, it is important that people be honest with themselves about their feelings. There are many support groups for this.
Recruiting:
There is no such thing as "recruiting" more gay people. The only thing that can be done is help people melt through their fears and prejudices to expose what they are truly about.
People need to change their attitudes.