[galaxy-dev] options from_dataset evaluation in workflow

Dear all, in one of my tools I'm populating a list of possible choices from a file in the history using the <options from_dataset> tag. Now using the tool as part of a workflow, the choices are not calculated at the setup stage, but I have to enter free-text and Galaxy seems to evaluate whether that's a legal choice only when the specific tool starts running (way down in my workflow). Is there any workaround for this behavior, so that choices are presented before workflow execution? Thanks for any help, Wolfgang