Lyo::OSLC::RTC::CM: How to add a new related artifact link to a workitem

I try to deploy the Lyo::OSLC::RTC::CM Perl module to manipulate workitems in our repository.

Now I want to add an additional rdf:resource to the rtc_cm:com.ibm.team.workitem.linktype.relatedartifact.relatedArtifact collection of a workitem.  However, the method workitemUpdate only seems to allow the manipulation of existing elements in the array representation of the resource collection, because it throws a

Invalid subscript,... It is larger than the size of the array

  at me.

How can I "push" a new link into the array?