Setting the Max Rows Displayed in the Filtering / Select Drop Down

Hi,

I am using the filtering select box (dynamically) and would like to set how many rows are visable when selected. By default, the list spans the entire length of the page and I would like it to only span a static length say 10 rows or 20% of the entire page. I have tried to set the "No. of entries" or override the .css by setting the height of the field but no luck. Any help would be appreciated.

Thanks,

Tim