Ok, I've kept working at it and finally figured out how to do this well. So for anyone who doesn't currently know how to install a LetsEncrypt SSL on a load-balanced application in Forge, here's how you do it...
1.) Install a lets-encrypt SSL on your load-balancer, as you normally would.
2.) At the time of this post, Forge does not allow you to create cron-jobs on load-balancers through the interface. No worries, you can add the CURL command (for renewing your SSL) to one of the web-servers behind the load-balancer.
3.) (Optional) For optimal security, delete your firewall rules on the servers behind the load-balancer. The only one you'll need for the load-balancer to access, is port 80. So create a new rule -> Name: HTTP, Port:80, and IP Address should be set to the internal IP Address of your load-balancer (It's the one in parenthesis on the top right-ish of Forge). Basically, this rule says only the load-balancer can access these servers and only on port 80.
4.) At this point your server goodness is all set up. However, your internal network is using HTTP. This is fine for security purposes, but causes Laravel generated links to be HTTP instead of HTTPS. To fix this, install and setup "fideloper/proxy". It will tell Laravel to take advantage of the proxy headers your Forge load-balancer passes to it, causing your links to turn back to HTTPS.
Further Reading: This setup gets a user from their browser to your load-balancer using HTTPS, but from the load balancer to your web servers uses HTTP. The network between your Forge load-balancer and it's web-servers is considered a private network, and HTTPS is not needed. This is a common practice called "ssl termination", and when done correctly is PCI Compliant. It allows your load-balancer to handle the SSL junk and simplifies the process of maintaining and updating your SSL certificate by keeping it all in one central location.