I canít see how you could do what mxracer wants without setting up the zip or postcode data set as a pushpin set and importing it. So basically I think the steps are as follows:
1. Plot any data value using Data Mapping Wizard (eg Area) for all zip code areas.
2. Export the data to excel
3. Read it back in using Data Import Wizard as a pushpin set, resulting in pushpins at the centroid of each zip
4. Calculate the route
5. With code use Find Nearby to identify all zips within 25 miles of the route and export these to excel eg.
Private Sub CommandButton1_Click()
  Dim objApp As MapPoint.Application
  Dim objMap As MapPoint.Map
  Dim objRoute As MapPoint.Route
  Dim Ws As Excel.Worksheet
  Dim lngItem As Long
  Dim sngDist As Single

    Set Ws = Sheets("FindNearby Along Route")
    Set objMap = GetObject(, "MapPoint.Application.EU.16").ActiveMap
    lngItem = 1
    Set objRoute = objMap.ActiveRoute
    Ws.Cells(1, 1) = "Postcode Sector"
    sngDist = 25#
    For lngItem = 1 To objRoute.Directions.FindNearby(sngDist).Count
         Ws.Cells(lngItem + 1, 1) = objRoute.Directions. _

End Sub
6. Re-read this data back into excel as a shaded map (possibly as a territory), resulting in the sausage shape along the route. Eyeball any zip areas where, although the centroids fall outside the 25-mile zone, they should still be included.