You don't mention exactly which version of Workflow you are using. With the release of the MP1 update for Workflow Solution 7.1 SP2 you can configure the displaying of the mobile pages in the web.config file of ProcessManager. You simply need to edit the MobileBrowswerStrings setting in the file. I don't recommend leaving the string empty, but setting it to something that you know will never show up in a User Agent string.