Instance migration with candidate

I have updated process definitions with new candidate groups. The newly created instances are working fine, but the existing tasks do not have the correct candidate groups and so are not being returned in the searches.
Do you have any advice for writing a SQL script to add the ACT_RU_IDENTITYLINK records?
Do you have any plans to include candidate users and groups to the Process Instance Migration tools?

I am thinking something along the lines of:
similar to .withNewAssignee(newAssigneeId)