I've been watching a bunch of YouTube videos on this and some of them do seem to confirm this. The e-tube software has a configuration page where it just shows you all the available buttons in the system and you can assign whatever function you want to each one. I saw one video where the presenter looked like he had an SW600 on the screen, but only one (and he didn't talk about it). But it sure seemed like if you had two, they would both just show up and you could assign whatever functions to them.

A couple of people have mentioned the newer SW610 switches, which might be different. I've read that those are just dumb contact switches, and have to plug into special ports on the main control levers. The main lever has all the smarts and is responsible for sending the commands. That still doesn't rule out being able to assign front der control to them, but you only can have up to two of those I think, when you'd really need four unless you're using synchronized shifting.

I just realized I have a bigger problem though. The bike I wanted to play around with for this project is 10-speed only at the moment due to my older wheelset. I know the old 6770 RD is 10 speed but apparently it's only available in short cage. I was hoping to run at least an 11-34 cassette (preferably 11-36). So that would mean upgrading to 11 speed in order to be able to use something like an RD-R8050 GS, which starts to kick off a cascading chain of upgrades which kind of alters my thinking a bit.