Unfortunately, it is not possible to do that. There are three generic content based modules - Generic Content, News and Blogs. Custom meta fields could be added only to these modules. Lists is not one of them which means that you could not add custom fields to it. The Lists module is based on the relation: title-content and it is not designed with the presumption it would need more fields than that.
Maybe you could try extending the RadEditor control which is also used for creating content. The control itself is quite powerful and has built-in capabilites such as snippet management, document management, common links feature and so on, which may make up for the lack of meta fields to a certain degree. For more information on RadEditor functionalities, see RadEditor Manual
the Telerik team