should specify more. if you are looking for non-vba way to do it, i don't think its possible.
Sort of manual, but you can have a helper column that has formula =if(value in column B = "", cell above + 1, cell above). This will basically give you incremental numbers each time you have a blank in column B. Then at the end of the list, you can add 2 of each numbers (starting with 2 - whatever max is). Copy and paste value that column. Sort on helper column and then by column B.