I think this note may address your question:
http://support.sas.com/kb/23218
There is a link in this note to a document showing examples of writing CONTRAST and ESTIMATE statements. Examples of computing odds ratios using these statements are given in that document. While an example using GENMOD is not specifically shown, the same method applies. You could easily change the example using the CONTRAST statement in LOGISTIC to use the ESTIMATE statement in GENMOD.
The answers to many questions can be found in the Samples and SAS Notes in our searchable knowledgebase,
http://support.sas.com/kb. You can use the search engine there to find the answers you need.