Note that many features are disabled in a protected document; there isn't
much you can do about it.

One way to do what you want is to not use forms protection; instead, you
could restrict the editing of the document to insertion of comments and then
set exceptions for the areas where editing should be allowed (in the
Restrict Formatting and Editing / Protect Document task pane).

Note, however, that you may find it easier not to use editing restrictions
at all. This depends on how you are using those fields on the cover page. If
you simply want to mark a location where data should be entered by the user,
you can use MACROBUTTON fields (see
http://word.mvps.org/faqs/tblsfldsfms/UsingMacroButton.htm.)