[galaxy-dev] controlling dataset formats in output collections

Dear all, as the title says I'm wondering whether there is any way to control the format of the elements of a collection generated by a tool. I know how to specify the type of the collection itself (list, paired or nested), but this is about the elements themselves. For example, I would like to be able to set the elements' format to fastqsanger or fastqsanger.gz directly in the outputs section of the toolwrapper. Thanks for any pointers, Wolfgang