What I would like to do is:
instantiate store -> call fetch to get the data -> at a later time, run queries on this already populated store to return by a particular attribute in the store.

For instance, this will populate the store:

var store = new dojo.data.ItemFileReadStore({jsId:"cacheFirst",
url:"getCache.php?test_ids="+test_ids+"&page_id="+page_id+"&min_time=first&max_time=first&order=ASC&limit="+limit });
var processCache = function(items,request){
cache_first = items;