I can't promise that the following code will work out-of-the-box as I'm working with only access to a text editor and the online help files, but this is the general idea.
grid = $find(
"<%= RadGrid1.ClientID %>"
selectedRows = grid.get_selectedItems();
i=0; i<selectedRows.length; i++)
o.FirstItem = selectedRows[i].getDataKeyValue(
o.SecondItem = selectedRows[i].getDataKeyValue(
//o.SomeOtherThing = some calculation or value added item, whatever yo want
result[i] = o;
I'm sure that a grown-up will be along to point out any errors, but that should get you going.
Please remember to mark the reply as an Answer if it's helpful.