It's on the list of things DW wants to implement: http://bugs.dwscoalition.org/show_bug.cgi?id=76

If you're logged in as the
main account, you should be able to comment as/update as/manage settings
for/etc any of the alternate accounts, preferably with inline AJAX that will
reload/redraw things (so you have access to userpics, tags, etc) without having
to load the Work As User menu and re-input your password.

As far as I know, this is also supposed to work for commenting etc.