If you are comfortable writing PHP and manipulating WordPress filters, you can override and customize your Asana workflow with custom logic.
You will need to have a Gravity Forms to Asana feed that will be your default case (who it gets assigned to, which project, etc.). Then you can have all the conditional logic you want in PHP to override those values based on certain conditions.
This simple example looks for form submissions marked with an ASAP priority and then makes the Asana task due today (whenever the form is submitted) and assigned to a specific user: