One option that would work is
Have the scroll bar option enabled, but set the line colour for the portal to match the background so that it is invisible.
You can add your own box to surround the portal if required.
Use a Global field for the portal row, depending on your version of Filemaker you can set an OnLayout Script trigger to reset this Global Field to 1 whenever the layout is accessed.
You can then use the Go To Portal Row (by calculation) option to navigate to the previous or next portal row by adding or subtracting from the Global Field.