GtkComboBox Displayed Items

Hello,

Does anyone know how to control the number of items shown at a time when 
a GtkComboBox shows its popup in response to a user click?  I have a 
couple combos for choosing State (so 50 entries) and they always take 
whatever screen height is available, including running right over the 
task bar in Windows.  The only difference between Linux and Windows for 
me is that Linux takes the entire screen height from top to bottom and 
Windows chooses the direction with the most space (from top or bottom) 
and expands in that direction all the way to the edge.

If there's no way to set this in terms of item height (e.g. such that 
say 10 items show at a time and the rest are scrolled to), getting a 
reference to the popup window itself so I could force a fixed height 
would still be much better than its current behavior.

-Jake Cobb