This has been the behaviour of eraser as far back as I can remember (long before heidi took over the project). You could always submit a feature request on http://eraser.heidi.ie/trac to get this working.
I think this is the most appropriate place to post this, so I will.
I've finally finished working out the Eraser API and implemented it in AutoIt3, based on the 5.87b1 portable Eraser.dll. I've created a Drop Target front end for it, that is 100% portable and posted it in the development section of PortableApps.com. The DLL itself still creates the "HKCU\Software\Heidi Computers Ltd" registry key, but the target takes care of that. It's posted here -
I'm finally very happy with the app. I just made an update today to improve, among other things, the Erasing report window. It's not a replacement for a commandline program, but any AutoIt3 devs should be able to create one easily with the API. Maybe I'll do one some day if I need it. All the source including the API comes with the package.
One more thing, according to Joel, it seems you *might* be able to use an older version of EraserL.exe (ie the 5.84 version before the VC++ requirements) with the 5.87b1 DLL. I have not tested this though, and the function names may have changed since then.