I have this same feature need. Seems like the only option is to manually copy the grades submitted by peers.
One possible workaround I have in mind is to have each group member submit the same groupwork assignment individually. and each submission then be graded by a different set of peers. This would allow the grades to be entered automatically but may result in students in the same group getting different grades for the same assignment. Depending on your students and the grading rubric, this may or may not be a significant issue.