jQuery Grid Plugin - jqGrid

I'm using the date formatter but also want to append characters to some of the cells, to do this I'm using  custom formatter.

I don't yet see an efficient way todo both.

Alternatively is there any way to reuse the formatoptions found in the predefined formatter?

I'd like a combination of the following formatters:

{ name: 'Amount', width: 30, sortable: true, align: 'center', formatter: 'currency', formatoptions: { decimalPlaces: 2, prefix: "$ "} },

and 

{name: 'Amount', width: 30, sortable: true, align: 'center', formatter: negativeNumberFormatter },

function negativeNumberFormatter(cellvalue, options, rowObject) {

        return cellvalue.replace("-", "($") + ")";   

}