vsftpd: use Explicit SSL in a different port than unencrypted FTP

I've managed to run vsftpd with unencrypted FTP, Implicit SSL, and Explicit SSL. What I'm looking for is a way to run it with Explicit SSL, but have a separate port for SSL. For example: port 15000 for unencrypted, and port 15001 for SSL. This is because I want to enable LAN users to connect unencrypted but WAN users to connect *only* encrypted. I would use SSL on LAN too, but I'll be going Gigabit soon (laggard) and having a couple of users transfer files at speeds 70-100MB/sec is going to bring my server's CPU to its knees. What has worked so far is to run two instances of vsftpd with different configs. I was hoping for a more tidy solution.