[galaxy-user] Workflows with parameters

Hi, I was talking about the Galaxy workflow with someone recently. He pointed out an "obvious" limitation of the workflows that I never realized before. So I thought I'd ask the team if any work is planned in this direction: In a workflow, the only part that is dynamic and configurable by the workflow user is the input files at the moment. I think it would be nice to allow setting parameters for some specific workflow steps. For example, say that my workflow involves running Megablast, as a workflow designer, I would be able to tick a box that makes the "word size" input be changed by the user when he runs the workflow. What do you think? Does this feature already exist? Are there plans to implement it? Regards, Florent