STOP! WE'RE ALL WRONG!!
First, I apologize. The "w" works just fine. What
isn't working on the provider line is *67 for some reason. Even if I attach a phone and dial it I only get a fast busy. That is relatively new behavior (and I'll bet I know when it happened) so I started using *70 for testing and left the phone hooked up and could hear it send the *70, then pause half a second, then send the rest of the number. And I'm pretty sure it was sending the *67 just fine as well, but the line wasn't taking it.
The <S1> might work but FreePBX hates it, and even when I tried a trick to force it, it was still dialing extra digits. A lone S (no 1, nor angle brackets) seemed to produce a one second (or so) pause.
Anyway, sorry to lead everyone on a wild goose chase, I didn't know that *67 had stopped working so now I need to investigate that.