Now that I could take a breather (it's been busy), I did some poking and prodding and found a way to enable the Debug menu in Safari for Windows. My first thought was that the settings were stored in the registry, but a quick inspection showed that wasn’t true (there’s no Safari entry in the Apple Computer, Inc. key in HKCU\Software and HKLM\Software). Next I went to the user’s profile and found the settings for Safari:

C:\Documents and Settings\[USERNAME]\Application Data\Apple Computer\Safari\Preferences.plist

This is an XML file, and you can add the following elements as children to the <dict /> element to enable the Debug menu:

<key>IncludeDebugMenu</key>
<true />

Save the file and restart Safari. It’s not as simple as running the defaults write com.apple.Safari IncludeDebugMenu 1 command in the Mac's terminal, but it’s easy enough to enable.

Update: The WebKit Project now offers nightlies for Windows, and that means we can use Drosera (Edit: hopefully someday), too.