how to create a RDS instance in VPC that is publicly accessible

I want to create a RDS instance in VPC using boto.rds, which is publicly accessible. But can't able to do so. it is by default no public access.

I know using boto.rds2 a publicly accessible instance can be able to create. but i want to do it using boto.rds Does it possible?

or

After creation of instance, modify it as publicly accessible using boto.rds2 also works.