Perhaps not the answer you were looking for, but you could write some post-processing VBA code that scans for long lines and inserts the symbol you want.
This code might get you started (it is copy-paste ready):
Sub FixCodeLines()
Dim p As Word.Paragraph
Dim c As Word.Range
Dim charcount As Integer
Dim MaxLineLen As Integer
Dim txt As String
Dim styname As String
MaxLineLen = 68 ' number of characters on one line
txt = " --> " ' symbol/text to insert
styname = "Code" ' name of style to process
For Each p In ActiveDocument.Paragraphs
If p.Style = styname Then
charcount = 0
For Each c In p.Range.Characters
charcount = charcount + 1
If (charcount Mod MaxLineLen = 0) Then
c.InsertAfter Chr(11) & txt ' Chr(11) = soft enter
End If
Next
End If
Next
End Sub
The code will, for all the Code-styled paragraphs, insert a shift-enter and the text of your choice after each long line (based on the number of characters)
How to use:
Apply the style "Code" to all your source code paragraphs (a good idea anyway not to use manual formatting). Make sure your Code style font is a fixed width font such as Courier.
Copy-paste the code in the visual basic editor of Word (type ALT-F11, click Insert > Module, and paste the code)
In your Word document, count the maximum number of characters on one line of your code code and change the value in the macro to that value (currently 68)
To execute the macro, back in your Word document press ALT-F8, select FixCodeLines and press Run.
Note that you can only apply this macro only once, there is no intelligence to detect paragraphs that have already been 'fixed'. So you should run it at the very end of preparing your document.
Also, if you have a more recent version of Office (2003 etc), you might have some troubles saving/executing the document/macro because of security blabla. Read all potential Word dialog boxes with care to avoid losing your code.