If your data is in column A then in column B put in this formula ="’"&a1. That renders your data permanently text. Copy and Paste-special as values back to column A. That’s a " with a ’ followed by another ".
When I try a similar exercise in Win Excel 2010, I have a (usually annoying) pulldown menu next to the paste area that allows changing how it was pasted, labeled “Paste Options”.
Within this menu is an option to use a Text Import wizard, just like you might in the “Data/Text to Columns” menu… delimiting and assigning format types by individual column.
Using that wizard, I can force a column full of slash-divided integers (which Excel stupidly assumes is a date) into Text (retaining the number/number layout) AS I PASTE. So it doesn’t initially get treated as a date (and broken in the process).
It seems to work, assuming the data you’re copy/pasting is structurally consistent enough. (same columns separated by the same delimiters)