Adding comment on behalf of another user

I'm wondering if this is possible. We are using SVN as our SCM system, since we are evaluating RTC. I've written a post-commit hook for SVN which will add your svn revision with a link to the diff to the work item you were working on. The post-commit hook will also add your SVN commit message to your work item as a new comment. Currently, this comment is being added by a user that is only being used for this sort of automatic thing. I was curious if it would be possible to still login as this user, but, have the comment be added on behalf of another user. So, for instance, if I committed to SVN, my work item would get a comment with my svn commit message and the comment would appear to have been added by me.

I'm looking at https://jazz.net/wiki/bin/view/Main/ResourceOrientedWorkItemAPIv2#Adding_a_Comment_to_a_Work_Item and in the example of reading a comment, it has the creator field. Can I set that when I add the comment? If so -- how would I get the rdf:resource URI given just the username of the user? Thanks for any help.