Since it is a sleeve, have you considered using a 16" circular instead? Sometimes I have laddering issues with dpns, sometimes I don't. I tend to find that the more I'm freaking out about something and over-working the problem (as I'm guessing from the amount of your swearing), the more it happens no matter what I do. If you do have problems with laddering with the circular, at least it is just at one spot and that's easily enough remedied.
The sweater is for a 6 yr old so there are not enough stitches for 16'' circular.
I've tried moving that join along, but it just looks loose and sloppy. I don't know if I can live with it. I might try to kind of wet block what I have to see if it helps. I would die if it looked crappy after finishing both sleeves. It doesn't help that the metal DPN are Susan Bates and weigh about 10 lbs.
I found the short Clover mini-circular in US10 (the only size they have- are they discountinued?) and ordered it today. I think it was meant to be since that's the size I need. If that doesn't work, maybe knit in the round on two long circulars?? I've never done it- does that help with laddering?