They added a new, easy way to do this and more with groups with anything but a “fixed” container layout (i.e. Row, Column, or Align to parent).
Just above the Margins section of the Layout tab there is a checkbox option that says “Allow vertical scrolling when content overflows.” Check this.
Add your long text box (or anything else that you want to be scrollable) into this group.
Next, limit how long the group is allowed to expand. (e.g. if your text box wants to be 500 pixels long and your group as an unlimited Max height or, say, a Max height of 800 pixels it will simply show the whole, long text box. If you shorten the Max height to 300 pixels, the text box is now too long to display all at once, so the group will gain a scroll bar and let your scroll down.
I just re-found this for myself today and am very happy about it =)
I hope this helps someone. 
And in response to:
2 Ways that come to mind (but i hope my previous explanation works better for you):
- Add a Type called something like “Text for Scroll Displays”
- Give it 2 Text fields
- Body Text (for the text you want to display)
- Name (a name for what this text is for)
- Manually create a new entry in your database for each instance of text you want to display
- Now go to wherever you want to display text and do a search for "“Text for Scroll Displays” and select for Name = (whichever entry you need)
- This will return a “list of Text for Scroll Displays” so take the :first item and that should be the text you wanted.
- You could add it in an option set such as “OS Text for Scrolling Text.”
- Use the display spot to name what the text is for.
- Then add another text field and put the text you wish to display there.
- Now use whatever approach you want (Multi-line input or Repeating Group) and for the data source, use “get an option” to select your option set and then select the right text entry, then select that entry’s Text.
(Thankfully this is not necessary )