With this sample file you can copy the style from my portal with no scroll bars and then apply this appearance to the portals in your own solution.
In FM12 you can set the width of the portal scroll bar to be zero pixels wide, making it invisible but still scrollable. This is a great technique for making a clean iOS interface. (In FMGO12 the iOS temporarily displays it's own thin scroll bars as you are scrolling.)
TIP: FileMaker does not let you manipulate the scroll bar's appearance within FileMaker Pro but you can edit a theme's CSS file or you can use a program such as Clip Manager 4 to alter the how a portal looks.