If you are using one drop down list you should be able to maintain the value using a session as you have said.
To do this, you will need to store a session when the submit button is clicked to store the value of the drop down list. And then for the 'Select value equal to:' in the Dynamic List/Menu you can use that session.
I have attached a page that demonstrate how to do this.
let me know if you have any questions.