Hi,
I have created jira issue for BPMC project (just to have it in the right place).
I did already implementation for that so user name is stored as process variable automatically and transparently (so to say to the initiator of the process).
https://jira.jboss.org/jira/browse/BPMC-65
Please vote for it, this could help to prioritize it and hopefully will be included in the next release of the console.
Cheers,
Maciej