Sigh. Well, one approach then would be something like 

    <glyph xml:id="conus">
      <desc>A <mentioned>&#xA76F;</mentioned> glyph used to
        indicate a <mentioned>&#xA770;</mentioned> character</desc>
      <mapping type="standard">&#xA76F;</mapping>
      <mapping type="orthographic">&#xA770;</mapping>
    </glyph>

So, not knowing any Latin, let's pretend "consensus" appears with the
glyph for LATIN SMALL LETTER CON both at beginning and end. Then it
would be
      &#xA76F;sens<g ref="#conus"/>
or
      &#xA76F;sens<g ref="#conus">&#xA770;</g>

> Thanks, Syd. The "con" glyph is used consistently for both "con"
> and "us", but "con" occurs only in word-initial position (49
> occurrences), while "us" (243 occurrences)is only word-final or
> (less commonly) -internal.