There's a situation where I want a particular kdialog window to always be above other windows. Right now I've used "System Settings > Window Behavior > Window Rules" to make a rule for this. However, this seems kludgy to me, and I'd prefer to do this by giving kdialog a command line option or environmental variable or something. Is there a way to do this?

Kludgy? No. This is the way to do it. Your window manager controls which window is on top, and if you want a window matching a set of rules always to be on top of others, you have to tell the window manager about that. It works the same for other window managers, too.

There is, however, ways to tell KWin to do this without using the GUI tools for configuring the rules; you can have a look at the kwin scripting API if you're interested in that.

Greetings,
Sven