SharePoint renders fields on a list view is with XSLT style sheets, so there is no method to override. If you want a your own way of rendering on list views, you need to create a custom XSLT style sheet named fldtypes_*.xsl and deployed it to (14 hive)\TEMPLATE\LAYOUTS\XSL.
- How to: Create a Custom Field Type (paragraph 3. (Optional) Create a Custom XSLT Style Sheet)
- How to: Customize the Rendering of a Field on a List View