Thanks for the responses, guys!
After writing the post I went looking online for some kind of solution. The closest I found that may or may not work is something called
"Steel Wire" from Sennheiser, which may or may not be the right connector. It does sort of look like the ones I have, and JTS is the OEM for at some of the Sennheiser line, but nowhere does anyone show the end of that connector, nor does the other end come from anyone with a TA4F connector, so it would have been a $60+ or so (each) gamble to even see if it would work
I was under a deadline, so the day after I wrote the post I came up with something that I hope works. I took pictures if you want to see it but a description might be enough.
When I got my Melodie speaker system it bugged me that the pins that hold the rigging system together were all loose; knowing how easy it is for me to drop things it became clear that they needed to be captive somehow. Each one has a little hole in it, so I took one to a place that sells wire rope and they had some plastic covered wire rope that fit nicely, and my buddy John Poulson showed me how to swage the ends, so all the pins were in pairs so one end stayed in while you were working on the other pin to set an angle or something.
That is relevant because, not knowing at the time how much length would be required (Meyer's weather protection hoods use the same or similar pins), I bought enough rope to do about a hundred pin pairs and still have a ton of it left over, probably 75' or so.
That stuff is tiny, light, and plenty strong enough for this purpose, so I taped it to the length of one of the headset cables, using e-tape, and left enough hanging out to make a loop that goes through the belt pack belt clip on the one end, and around the headset on the other end.
The belt pack end has the added bonuses of keeping the spring clip attached to the pack (the clip springs out to disconnect, and the cable should hold the two sides toward the center), and by sizing the loop orientation carefully it runs right past (touching) the TA4F knockoff while it's plugged into the pack. I put some Shoe Goo, which I've found to be a rugged adhesive/caulk/hole filler, between and around the cable and the non-release side of the connector in hopes that the belt clip will take the strain of a pack drop rather than the connector. At the least, the connector will pull out of the pack when pulled rather than the wire pulling out of the connector. I hope.
At the other end, the headset itself seems plenty rugged enough, so that loop goes around the metal headset wire frame next to that connector, and I put some other twist-tie type vinyl covered wire (from Monoprice) to keep the loop from sliding away from the connector and pulling on it.
There is still a weak point where the original wire comes out of the tape and attaches to the headset, but I'm not sure how to deal with that.
Subsequent to making those (two of them), I remembered some small nylon braid mesh sleeve that was left over from another project, and had just enough to do one more assembly. The e-tape wrap is inside that mesh, and looks pretty good.
The mesh I had was really heavy duty, so the whole thing is pretty thick but it doesn't weigh anything, at least to my way of thinking. I have some smaller lighter duty mesh on order, so I'll be ready to make some more. FYI, it's black, and so was the e-tape. Also FYI, I smeared black Shoe Goo over the ends of the mesh tube, and it just came out seeming like a black tube that stays in place. We'll see how it lasts.
I decided on black e-tape because I figured white e-tape would show dirt more, and these things have to get dirty from handling/clothing if they don't break first. My hope is to get a year or more out of them, but we'll see.
Total new out-of-pocket cost for two cables: $0. So that was nice.
They are at the client's now and have been since Monday. No news from them is good news?
Thanks again for the replies, and maybe we can come up with something to help others in this situation. I'm not going to claim that this solution (if it actually works) will work for everyone, and maybe not even for anyone else.