Command-line multi-thread rendering switch?

Is there a command-line override switch for the threads button in the render settings? I have a .blend saved with threads enabled and was wondering if there was a way to switch that off when I render the file from the command line.

Scenario/reason: I’m patiently running an animation that’s taking a very long time (5+ hrs/frame, typically, because of motion-blur) so I’m rendering a couple/few frames out overnight on my dual-proc system (and more on weekends.) However, I could run a one-thread render during the day and still have a workable system to get stuff done on. I just don’t want to have to open up the file, switch the thread button, save and close it every time. (Lazy a$$? You betcha! Would I forget to change it back? Darn straight!) Thot maybe I’d pop this in the dev forums as a feature request if no-one knows a trick.

hmm, is there any problem rendering with threads, although the CPU doesn’t support them? it works, and i don’t think it is actually slower. Someone ought to try it out, or ask someone else who really knows it.

I did an informal test, and having threads enabled on a processor that doesn’t support it makes it slightly slower. That’s why there’s a button for it, and it’s not pushed by default.

Also for the thread starter, here’s an idea:

Leave the threads on, but then start “top” and renice Blender to level 2 or so. That way Blender will only hog the CPUs if no other apps want it. That way you get the speed of threads, and a responsive system.

What is “top”? I’m on Windblowz… is it an app that runs for this OS? Also, if so, would it allow me to allocate which proc I want a given thread to run on? (Doubt that’s possible here, but WTH… thot I’d ask.)