I want to restore my device without using the iTunes GUI (or Xcode),
but I can't get idevicerestore to work on OS X.

This is a compromise - a simple command-line client for the restore
functionality in Apple's MobileDevice framework.

To activate the device after restoring, ideviceactivate does work
on OS X; here are some binaries if you want:
http://a.qoid.us/ideviceactivate-etc.tar.bz2

Note: If you're in DFU mode and uploading iBSS fails (e.g. because
it's a PwnageTool ipsw but you didn't enter pwned DFU mode with
redsn0w or PwnageTool first), this tool will get into an infinite
loop with a lot of text scrolling down the screen.

On the other hand, it will sometimes take a few seconds with no
visible progress, so be patient.

Note 2: This likes to crash TinyUmbrella for some reason.