It appears you can only pick up a syndicated feed if you're a paid member of DeadJournal… I posted a support request and got this reply:
You cannot customise the appearance of the feeds journal in any way. You simply created it, you do not maintain it.
Only paid accounts may add syndicated feeds to their friends list. This is because, to add a feed to your list, you must use some syndication points. Free users have no syndication points, whereas paid users have 5.
Full request'n'reply exchange here.
So… who wants their account paid for? (potters off to look up his PayPal password) :o)