Assign primary parent

I have the following menu structure:

Main Menu
-Our Services
--Cancer Center
---Radiation Oncology
----ACR Accreditation
----State-of-the-Art Technology
--Medical Imaging
---Radiation Oncology

I create a menu item for Radiation Oncology with the parent of Cancer Center. And then I create a second menu item with the parent of Medical Imaging (both with the module interface within the node).

I want the user to be taken to the menu item with the parent of Cancer Center (showing the Cancer Center part of the menu tree) and have the sub links displayed - regardless of which link they click to get there.

The only way I can currently find to do this is to have the menu item with the parent of Cancer Center added last. The module seems to assign based on the most recently added menu item.

This is proving to be incredibly inconvenient as it is almost always the first item added that should be the primary parent, not the last menu item added. It also means that to configure my menus correctly, I need to delete and re-add menu items - and then re-assign it's child page menu items, which is obviously less than ideal.

I hope this makes sense.

Is there a setting somewhere that I am missing? I've tried adjusting the weights and it doesn't seem to make a difference.

***It would be very nice to have a radio button or some way to select which menu item should be the primary parent.***

(I am also using Menu Block - if this affects this any way, I'm not sure.)

Thanks!
Stephe