Unfortunately this can not be done on multi-line fields. This holds true for both RTF enabled fields and multi-line plain text fields.
This is by design (and actually makes a lot of sense), as trying to limit text is normally to do with the amount of space used by the text, and these fields support line breaks (and other formatting in the case of RTF enabled fields) so the string length has little to do with the space used by the text.
If your field is an RTF field, you could write a "Truncate" XSLT to apply to the text. Otherwise you will need to use one of the solutions you have referenced above.
Alternatively you might consider truncating the text with your output templates if it is too long.