Close Combobox List On Mouse Exit

On a userform I am using the MouseMove event to dropdown a combobox list. When I move the mouse away from the combobox the list remains dropped down. I want the list to close when the mouse moves away as it hides other controls on the form.
I have tried using MouseMove when over the userform or transparent labels around the combobox to set focus to other controls but this does not close the combobox list. The only way to close the list is to click away from the combobox. I have looked at how to simulate a mouse click but that is beyond my limited understanding of vba. If this is the only way to achieve the required result then I need some patient assistance. I am using Excel 2000 on XP.