How to Route Elastic Beanstalk traffic through a Single IP for External API

I have Application deployed on Elastic Beanstalk and it need to make call to an external API Server which can reply to only single IP. AutoScaling is in picture. So I need to Route all my OUTBOND traffic through a Single Server. So that External API thinks that Request is coming from a single IP. May be by using NAT or any Proxy Server or VPN.