This is what you can try with JQuery:
To insert fixed format after some row (say 1st):
$("#tbl tr:nth-child(1)").after('<tr><td></td><td></td><td></td></tr>');
To insert a copy of some row (say2nd) after some row (say 1st):
$("#tbl tr:nth-child(1)").after($("#tbl tr:nth-child(2)").clone());
Hope this helps.