Adjusting theme switcher functionality

I’d like to adjust the functionality of Theme Switcher to select themes via URL using “index.php?wptheme=”

Currently, the function checks if there is a Theme Name specified in the stylesheet. If there is no Theme Name, it allows you to select theme by directory name. I’d like to set it so that it only selects themes by directory name and ignores the stylesheet. Any pointers on how to accomplish this?