Sorting on hidden columns

Hi,

I've configured a datatable with various column filters, my clients have now asked me to hide some of the columns but they still what to be able to filter on them.

So my 'aoColumns' is as such

"aoColumns" : [null,null,null,{ "aDataSort": [10,0], "aTargets" : [3] },null,null, null, null, null,{ "iDataSort": 11 }, {"bVisible": false}, {"bVisible": false}],

(The last couple of columns are hidden, which I'm using to sort on dates, etc). And my filters are :

.columnFilter({ sPlaceHolder: "head:before",
aoColumns:
[
{ sSelector: "#titleFilter", type: "text" },
{ sSelector: "#practiceFilter", type: "string"},
{ sSelector: "#typeFilter", type: "select", values : ["Conference", "Course", "Webinar"] },
{ sSelector: "#dateFilter", type: "date-range" },
{ sSelector: "#regionFilter", type: "string"},
{ sSelector: "#cityFilter", type: "string"},
{ sSelector: "#cpdFilter", type: "number-range"}
]
});

Now if I hide the second column (using "bVisible" :False), the whole of my filtering goes mental (!) is there anyway way around this does anyone know?

Thanks,
Craig