Loading 10k+ rows of JSON into jqGrid 1k rows at a time - jqgrid

Question

Introduction
I load a JSON object via ajax into the browser outside of jqGrid. I then load the JSON into a grid, which the initial setting datatype: "local", using the following:
$("#myGrid").jqGrid("setGridParam", {datatype: "json", loadonce: true});
$("#myGrid")[0].addJSONData(jsonObject);
$("#myGrid").jqGrid("setGridParam", {datatype: "local", loadonce: true});
The above tricks the grid into allowing me to load a JSON object without the jqGrid making an automatic call for it (which is its default behavior).
Implementing server-side pagination would be ideal, but not currently feasible in my case.
The Question
I need to load about 10-20k rows into the grid from JSON. But that takes several seconds. To boost performance, I'm trying to add 1k rows from a JSON object at a time (which is fast and doesn't stall the browser), but I can't figure out how to do that with a JSON object on my hands. Here is my attempt, which loads the first 1k rows into the grid, but doesn't properly update the pager, and doesn't allow me to add additional rows via addJSONData.
$("#myGrid").jqGrid({
jsonReader: {
page: function(json) { return 1; },
records: function(json) { return json.records; },
repeatitems: false,
root: "objects",
total: function(json) { return json.totalPages; }
},
// . . .
}
$.jgrid.extend({
loadJsonFirstPageOnly: function(json) {
return this.each(function() {
// copy the first page of data into a truncated JSON object to load into the grid
var resultsPerPage = $("#" + this.id + "_ResultsPerPage").val();
var numberOfPages = parseInt(json.objects.length / resultsPerPage);
var firstPageData = {"objects": [], "pages": numberOfPages, "records": json.objects.length};
for (var i = 0; i < 1000 && i < json.objects.length; i++) {
firstPageData.objects[i] = json.objects[i];
}
// load the truncated JSON object into the grid
var $this = $(this).jqGrid("setGridParam", {datatype: "json", loadonce: true});
this.addJSONData(firstPageData);
$this.jqGrid("setGridParam", {datatype: "local", loadonce: true});
// adjust the grid's internal state
this.p.allData = json;
});
}
});
Any thoughts? Thanks!