I suppose I could shop around for a doctor willing to prescribe modafinil for my sort of sleep problems.

Do it. Even if your underlying condition is incurable some of the symptoms can be managed. And Modafinil is outright brilliant for managing fatigue and supplying wakefulness.

I have thought of trying it in the past, but that's pretty far off-label.

Compared to the most prominent usages of modafinil (performance enhancement) your usage would be pretty damn close to the label all things considered. But forget the label. Tell the doctor whatever is convenient to make him sign stuff for you. (You do keep your doctors separate, right? The ones who give you actual useful advice and the ones you use as gatekeepers to the system. Lie to the latter.)