I think the suggestions that you read were for getting a dynamic value into the select list, that is not what you should be trying to do here. Instead you should just be setting the selected value based on your session variable. To do this you would select the list in design view and in the property inspector click on the dynamic button. In this interface use the lightning bolt icon next to the 'Select value equal to' field to select your session variable that holds this value. I'm including a screen shot of what this dynamic interface looks like for a select list for your reference.