Thing is, I have a RR501 (two, in fact) sitting around doing nothing.

I'm not looking to go out and buy an appliance module...I'm trying to
use up stuff I've already paid for and have no other use for.

If I can't find the steps to modify the RR501, I'll just go with the
nightlight solution, another item that I have lying around doing nothing.

Thanks anyway!

I might try removing the 220K R44 which appears to be the sense
resistor. I don't know if this would cause other problems. For all I
know, it might need the feedback that the module is off or on in order
to hold the relay, or something crazy like that. That said, I did a
similar thing when modifying lamp modules into quiet appliance modules.
But this was a lamp module, i.e. no relay. There are 2 such mods on
line. One uses a solid state relay; the other uses a zero crossing
detector opto isolator. Both seem to work well, but as I didn't want
the sense current messing with CFLs or LED lights, I clipped one end of
the resistor in the sense path and it worked. Of course, heed all the
danger warnings you read about working in X10 modules.