I am sure that there is more than one way to accomplish this but the challenge was to differentiate between a user opening the record using the URL from the email versus opening the ticket from standard UI navigation (in which case we would want to suppress the auto-assign functionality).
The best way to achieve this seemed to be by adding a custom URL parameter that we could then manipulate via jscript to perform the necessary processing. However by default if you try and add custom parameters, the form will error out when you try and load.
Luckily, I discovered a blog entry which explained how to go about enabling the feature in the application. Believe it or not, you have to add a registry setting in order to allow this. I am not sure why there would be reason to suppress this in the first place but then again - if I had penny for every time I've wondered why certain features were designed in certain ways (MSCRM and beyond)...
Once this setting was in place, I could then add a URL via workflow containing the custom parameter:
And bob's your uncle! Well almost - of course you need to design the jscript on the form to retrieve the URL parameter (use the code snippet from the referenced blog) and perform the necessary logic to apply the update.