No we don't use the data object definition (only for the web service task we do). We make use of process variables and simple expressions to access them.
I have a prototype for this and have submitted it for consideration as a seed for extended support in the future. I cloned ACT-620 which was closed and posted the details here:
We're a bit behind with JIRA issues, but we are doing a sprint in the coming days. That will also include this issue, so we can see if we can include it for the 5.15 release.
