I located a solution here for adding the 'Open Command Window Here' option to the Context Menu for Library Folders.
You just have to add a few registry keys:
HKEY_CLASSES_ROOT\LibraryFolder\background\shell\cmd (set value to what you want to be displayed on the right click menu, e.g. "Open command window here"
HKEY_CLASSES_ROOT\LibraryFolder\background\shell\cmd\command (set value to "cmd.exe /k")
If you're not familiar with the registry editor, you can just copy the following text into Notepad, save it as whatever.reg, and double click it:
Windows Registry Editor Version 5.00
@="Open command window here"
I did it in a slightly different way, exactly copying the keys and values that appeared in the cmd key within the Directory/background folder. The result is a little different, as the command window is opened at the location you expect (the current folder), rather than "c:\Windows\system32" as with the above.
@="cmd.exe /s /k pushd \"%V\""
To address the comment by @Zoredache, this ambiguity only exists when the folder you are viewing is the union of folders, as indicated when the header section of your folder has something like this.
In this case, the location that the command window opens to is whichever directory in your Library is set as the 'Default Save Location'. Other than that, it behaves as-expected.