I suppose you could assign a pair of macros to a keyboard shortcut.
Something like:
Sub SelNextSen()
If Selection.Sentences(1) <> ActiveDocument.Sentences.Last Then
Selection.Next(Unit:=wdSentence, Count:=1).Select
Selection.MoveEnd Unit:=wdCharacter, Count:=-1
Else
ActiveDocument.Sentences.First.Select
Selection.MoveEnd Unit:=wdCharacter, Count:=-1
End If
End Sub
Sub SelPrevSen()
If Selection.Sentences(1) <> ActiveDocument.Sentences.First Then
Selection.Previous(Unit:=wdSentence, Count:=1).Select
Selection.MoveEnd Unit:=wdCharacter, Count:=-1
Else
ActiveDocument.Sentences.Last.Select
Selection.MoveEnd Unit:=wdCharacter, Count:=-1
End If
End Sub
See:
http://word.mvps.org/FAQs/Customization/AsgnCmdOrMacroToHotkey.htm