Does anybody know how to use a rendering control on the display form? According to Microsoft it is possible but they don't give any hints on how to it. A link to an example would be excellent, but I have not been able to find any.
The first line of the following Microsoft article says it can be done.
I found a clue here http://social.msdn.microsoft.com/Forums/en-US/sharepointdevelopment/thread/4f4e734d-d7d1-4392-ab73-93ba23f3b542
According to the above forum the following two function need to be overloaded.
UpdateFieldValueInItem in basefieldcontrol and GetValidatedString in SPField class