any way to get rxvt to recognize shift+tab?

I'm simply trying to get shift+tab to be a recognized key sequence during my rxvt terminal sessions. So I can map it to usefulness such as:

bindkey "\e[Z" reverse-menu-complete

But, based on my research, I'm pretty sure the answer is no. Just want to make sure.

This is a hard limitation of rxvt? (Is there a technical reason for this limitation? Or just an unsupported feature?)

I can't get it to emit that either, although strangely enough, the rxvt source code (as shipped with Cygwin) does appear to have support for it:

case XK_Tab:
  if (shft)
    STRCPY(kbuf, "\033[Z");
  else {
    ...

Anyway, rxvt development stopped eight years ago. Try its successor, rxvt-unicode, aka urxvt, where this does work. If you're on Cygwin or MSYS and you were using rxvt without an X server, which urxvt does require, try mintty.