jQuery Grid Plugin - jqGrid

We are able to populate the JQGrid with on MVC 3 project. We use the   MultiSelect = true 
option for checkboxes. Now we want to check few rows inside of the JQGrid and make those specific rows available in the MVC controller on a button click event (Both button as part of Grid Toolbar Eg: MyGrid.ToolBarSettings.CustomButtons.Add(new JQGridToolBarButton...)  && Button which is not part of the JQGrid Eg:    

 <% Html.BeginForm("ExportRows", "Rows"); %>         
        <br />
        <input type="button"  id="Button1"  value="Export " onclick="this.form.submit();" />      
        <% Html.EndForm(); %>

How Do I acheive this since the checkbox column is not part of the Datasource Field or we have not specified any specific column in the Model for Checkbox column. Its just the Multiselect Property thats is used to show checkbox.

How to retreive checked Rows in controller on button click ?