Inserting an instance of replicant using formapi

cheeku

I am inserting instances of replicants with Formapi by using the following:
parent.datacapture.insert(item_after_which_to_insert.itemImpl.getInstanceID() + 1);
item_after_which_to_insert is the last item of the replicant instance after which i need to insert.
Now this is failing if i need to insert an instance of a replicant that has a replicant inside it.
If i pass the last item then the inner replicant instance is added and if i pass the inner replicant then nothing is inserted.
Following is my code:
var testItem = IWDatacapture.getItem('/cntDownloadSection/repGroupOfDownloads[1]/repDownloadsLinks[1]/chkBUtarDownloadsText');
parent.datacapture.insert(testItem.itemImpl.getInstanceID() + 1); //adds instance repDownloadsLinks

var testItem = IWDatacapture.getItem('/cntDownloadSection/repGroupOfDownloads[1]/repDownloadsLinks[1]');
parent.datacapture.insert(testItem.itemImpl.getInstanceID() + 1); //does not add instance of repGroupOfDownloads

how can i add the instance of the outer replicant?