You can do this easily using custom formatting in your column model.
Custom Formatter is a javascript function with the following parameters:
cellvalue - value to be formatted
options - {rowId: rid, colModel: cm}, where rowId is the identifier row colModel is the property object for this getted column from the colModel jqGrid array
rowObject is row data represented in a format defined from a data type
Thus, a function can be declared like this:
function myformatter ( cellvalue, options, rowObject ) {
And is defined in your column as follows:
{name:'price', index:'price', width:60, align:"center", editable: true, formatter:myformatter },
So, in your case, you can use the rowObject parameter in custom formatting to populate your extra values. For instance.
Column model
{name:'employee_id', index:'employee_id', width:60, align:"center", editable: true, formatter:myformatter, label:'Employee' }
Formatter
function myformatter ( cellvalue, options, rowObject ) { return cellvalue + ' ' + rowObject.email + ' ' + rowObject.user_name; }
And if it is defined in the employee_id column, it will be displayed in the cell:
employee_id email username
Here is a jsFiddle example showing that it works.