Is the section of text you want inside a parent tage of any sort a <div> perhaps? If not you could select the <body> tag and then do a regex on the returned HTML to isolate the text, then put it into a span.
var text = $('body').html();
var regex = new RegExp('regex pattern here', 'ig');
var arr = regex.exec(text);
If your RegExp has brackets surrounding various different sections of the code they would now be stored in $1, $2, $3 etc. So you could now re-build the html with a span tag around the text:
var html = RegExp.$1 + '<span>' + RegExp.$2 + '</span>' + RegExp.$3;
Where RegExp.$1 is all the html of body before the text you want to isolate, RegExp.$2 is the text you want to isolate, and RegExp.$3 is all the html after the isolated text.
That should do the trick.