Select Hidden List Items with Growing=True - sapui5

Question

I've a sap.m.Table with growing(true) and growingThreshold set to 5 and MultiSelect mode. Say, at any moment, the number of records in my JSON model is more than 5 (say 20). Hence, it will always do lazy loading.
I've a button which needs to select all the elements in my model i.e, 20 items. So, on click handler of a button i say : - table.selectAll().
Now, I since only 5 items are shown in UI ( and in DOM), the UI5 library only selects which ever elements are shown.
console.log('How many items selected ?', oTable.getSelectedContexts(true).length ) // says 5. But it needs to be 20.
Question is - How do I select all items without loading them in UI ? Showing all elements to just select them does not make sense to me.
Now,
User will not click load more so many times to load all elements. There could be 100s of elements in real scenario. How to select all n elements in model ?
I do want to keep additional property in my model just to mark a item is selected or not ? Any suggestions are welcome.
User can select-all initially and then de-select few items which he doesnt mean. So, 20 items selected and say, removed first 2, so total no of selections should be 18. Any suggestions are welcome.
Code:
<ToggleButton text='Select All' press='onSelectAll'/>
<Button text='Submit' press='onSubmit' />
<Table noDataText="No Data" id="table0" items="{/}" mode='MultiSelect' growing='true' growingThreshold='5'>
<items>
<ColumnListItem type="Active">
<cells>
<Text text="{id}"/>
<Text text="{name}"/>
</cells>
</ColumnListItem>
</items>
<columns>
<Column id="column0">
<header>
<Label text="ID" id="label0"/>
</header>
</Column>
<Column id="column1">
<header>
<Label text="NAME" id="label1"/>
</header>
</Column>
</columns>
</Table>
Controller :
onInit: function () {
var aData = [];
for(var i =0;i< 20; i++) {
var element = {
id : 'I00' + i,
name: 'Clone-' + i
};
aData.push(element);
}
var oModel = new sap.ui.model.json.JSONModel(aData);
this.getView().setModel(oModel);
},
onSelectAll: function (oEvent) {
var oSource = oEvent.getSource();
var oTable = this.byId('table0');
if (oSource.getPressed()) {
oTable.selectAll();
} else {
oTable.removeSelections(true);
}
},
onSubmit: function() {
var oTable = this.byId('table0');
console.log('How many items selected ?', oTable.getSelectedContexts(true).length );
}