Take a look at the text formatting functions. You can set up an auto-enter calculation to reformat the pasted data.
Define the text field(s) with: TextFormatRemove(Self). Then use layout settings to format the field with the desired format.
Use the other text formatting functions to specifically add the needed formatting to the data in your field(s).
In both options, be sure to clear the "do not replace existing value" check box.
Both can produce identical results when browsing/printing/previewing the data, but you can get different results should you export or copy paste from FileMaker to a different application--so you may want to test both options to see what works best for your situation.