Hi tonizz,
look at WCM2_1-Product-Evaluation-Guide.pdf. You'll see the extras-wcm/forms/press-release.xsd web form. This web form have a field that is the product of a jsp call.
<xs:include schemaLocation="/media/releases/get_company_footer_choices_simple_type.jsp"/>
This jsp is used to produce dynamically the type company_footer_choices, i.e. produce dinamically a listbox with a list of items.
IMHO I don't like very much this solution, but I think you can put inside the jsp every kind of logic do you want to produce a new type with the unique value you need.
Bye,
Vincenzo