There are a lot of switches available which can be added to the Dex.ini file; Leslie Vail did a post back in February 2014 where she listed all of the switches she knows (and a long list it is too).
I need to have a proper through Leslie’s list again soon as there are some very useful switches. Two that caught my eye recently, which are on Leslie’s list, were actually posted by Béat Bucher on the Dynamics Community Forum (I was searching for something else when I found the post):
SQLLastDataSource=Dynamics GP
EnableServerDropDown=FALSE
These switches set the last DSN used and then disable the Server drop down to stop users changing it. This is useful when there are several DNSs created on the client machine (required for other applications), but only one of them is for Dynamics GP.