Forms :: Split Form Combobox Requery Based On Row Selected

I have a split form that was not made by wizard. On the form part I have a combobox that is unbound to the form data set. The combobox has a query row source that is based on the current row selected. I want the combobox to have an up-to-date result based on which row is selected.

If I set the combobox to requery in the form_current event then I get what I want. I don't want to put up with the little delay that is generated every time a user changes rows because of the requery, though. I only want the requery to happen when they use the drop-down menu.

I have the requery in the gotfocus event of the combobox on the form. I mostly get what I want this way, however if they select an item in the drop-down list, then choose a new record in the datasheet, then try to use the combobox again, the combobox is not refreshed (because it never lost focus?).

To get around this, I've tried to setfocus to something on the form in the on_current event, but access gives me an error: 'Access can't move focus to the control btn_Refresh'.How can I get the combo to requery only when users are about to use it?