with fibro let me just say with fibro like mine. I couldn't do it
I'm not sure what the problem would be, esp. for the lower back and thighs.... have you got joint arthritis or similar, or very short arms?
I get to every spot I need to. I also didn't think I'd be able to, but it's easy.
There are a few spots in the middle of the back where I don't hold it, I
rest it on me. But then I often do that anyway cos it's less strain on the wrist, biceps, elbow, shoulder.
As opposed to the massage stick it moves, = does the job, by itself.
Even if that didn't work I'd use it like I use rods or corners to press into, I'd put it into some kind of a vice and hold myself against it.
And as has often been the case to do one kind of treatment I needed to do another kind first, in this case if I weren't able to get my hands behind my back well I'd work on that, with everything - exercises, stretches, pressure and massager. This may well also improve the back problems, because arms and shoulders are connected of course. In fact I think we can generalize that: With our amount of symptoms we need to prioritize anyway, and whilst your back may be the most painful, it isn't the first that should be addressed if you couldn't get there. But you doing the spots you can do, you're improving things so that you can do the other spots too. Maybe there are some you wouldn't even sense/think of doing, cos they're stiff rather than painful normally, only become painful when you try to hold the massager, but then these get a higher priority.
BTW, diagonally it's more than a foot long, plus I don't have particularly long arms I think.
But maybe I haven't thought of what might be the problem...?
When my wife occasionally uses it on me, it's "nice" for us, but by far not as helpful as when I do it myself. That's why I prefer self-treatment to physio treatment.