Hopefully Last CM Ribbon Question

Thanks to excellent help from this forum I have managed to get a child record entity form in a pop out window from a button click. (code below).I managed this by hardcoding in the ID for a specific record. How can I change this so that I gets the id from the parent entity.

In the parent entity the lookup is new_OAccounts and under SQL the value is CE993713-EBAE-E311-93FD-00155D04FA2A

In the child entity the field is new_originatingaccountsid  and under SQL the value is CE993713-EBAE-E311-93FD-00155D04FA2A

function openDirectDebit()
{
    var clientURL = Xrm.Page.context.getClientUrl();
    //Set features for how the window will appear.
    var features = "location=no,menubar=yes,status=no,toolbar=yes,width=2000px,height=600px";
    // Open the window.
    window.open(clientURL + "/main.aspx?etc=10014&extraqs=formid%3d0c6b8f80-3c48-43d0-afef-1a0890d30431&id=%7bCE993713-EBAE-E311-93FD-00155D04FA2A%7d&pagetype=entityrecord", "_blank", features, false);
}

Dont ask me .. i dont know