Dynamic Dropdown Range Rules

Hello, I was wondering if checking for a range in a dropdown list is possible with a dynamic dropdown. Here is the way the dropdown is populated.

$form->dropDownListRow($model,'images',ImagesToChoose::getImage($rad,$op), array('class'=>'span5 chosen-select', 'prompt'=>"Choose Image"));

Now I want to ensure the user only sends things from that list, so I want to set a range in rules. The problem is the fact that the method used to grab the initial list changes based on the parameters. Is there are way to redefine the rules after everything loads? Thank you