The only way to do what you describe is to make the first choice in your drop down field either blank, or say "Select A Product" and then enable values and leave both it's value empty as well as the price empty (empty is not the same as $0.00 in the price).
With the value empty this means the field will not validate as required if you set it as required and with the price empty it will not be able to be saved a real product selection (if the field was not required).
That is the only way to accomplish what you are trying to do using built in features and is the standard way to implement a drop down placeholder.
Beyond that if this for some reason doesn't work for what you are trying to do you would either need to be creative with how you use the available features and functionality, or use available hooks and write your own customization using custom PHP.
I did not see an explanation as to why this route doesn't work for you other than that it involves conditional logic. If you can explain what exactly it is you are trying to accomplish I may be able to suggest alternatives.
Posted 9 years ago on Wednesday March 7, 2012 | Permalink