The Force IDE opens the Apex class in an Apex Editor. This editor doesn't appear in the list of contexts that you can correlate with a key event. So, for example, a list contains contents such as 'editing in a structured text', 'editing in Java Source', etc. Your apex editor doesn't contribute a 'Source' menu option to the right-click menu. So, there is no way to get to the formatting features.
I attempted to open the apex class in Java. Now, the 'Source' menu option appears the format option doesn't do anything.
The one and only thing I can get to work is this:
Select file > Open with > Other > Locate Java Editor.
Once the file is open,
select all text ( right click) > Source > Correct Indentation
This doesn't reformat but it does fix the indentation problem.