Navigation sub-menu question

[antipodean]

Is there a way to hide sub-menu levels so that they will appear in the simple nav table but not in the main nav table?

EG: if I have a main menu item with structure to four levels deep, is there a way of limiting the number of levels shown in the main menu (using NAV_TABLE_COLUMN) but not hiding the deeper levels from the sub menu (using NAV_TABLE_SIMPLE) ?

This is really so as not to make the Main menu too complex (and hence, messy)