Custom datatable sort

Custom datatable sort

I have a table of data that is order by rank which can be entered through
an input box.
The rank is a single digit number 1 through 9 or it could be blank. I want
the blanks to always appear at the end of the list whenever I sort.
See the JSFiddle example: http://jsfiddle.net/afEHc/
If I use:
"aoColumns": [ { "sSortDataType": "dom-text" }, null ]
It works picks up the new values but the order is incorrect. That is the
blanks need to always appear at the end.
If I use:
"aoColumns": [{"sType": "data-rank"}, null ]
It works correct initially but then breaks when either I sort by another
column first or add a value to the rank column.
Any point or suggestions would be appreciated.