What are some reinforcing consequences you can deliver either immediately following the desired behavior or following a shift– things that this particular student enjoys, wants, seeks out, etc.?
You might adjust the sequence of tasks so that a particularly difficult task is followed by a break initially. Be sure to provide and teach desirable options for break activities that will be interesting to the student and appropriate for the work setting.
Are you using labeling and social praise to make the contingency between desired behavior and reinforcing consequence clear to the student?
In some cases, the student will try to seek out too much confirmation from supervisors and co-workers, possibly creating tension on the site. Consider scheduling specific times when someone will give feedback on performance so that the student can predict when he will learn what he is doing well.
What reinforcing consequences can you arrange that are more naturally or intrinsically connected to this targeted behavior?