Legally, you can't. Period. A birth certificate is meant to be a record of the BIOLOGICAL parentage of the child, not a record of who you like best this week.And I'm pretty sure I can put my significant others name on there, I just need to know how I can do it legally.
Putting your current boyfriend on the birth certificate is not only paternity fraud, but completely stupid. You've known him a couple months. What happens if you break up? You think you'll get to put the next boyfriend on? He knows the child isn't his, but do you REALLY think he'll jump all over paying child support if you break up?
I'm sorry your ex is abusive, but this is not going to solve the problem. Leave the "Father" field blank.

