Wonder if any of you kind Londoners can help me out here.

As someone who visits London frequently, I already have an
(unregistered) Oyster card, which I top up from time to time with
little bits of cash here and there. In a couple of weeks though, I'll
be going to London for a work-related visit.

To save money, I'm intending to use the Oyster card. Is there a way I
can get a print-out of my journey history, to show to my boss, so I
can claim expenses back? Do I have to register my card for this, or
can I obtain a print-out from a ticket office, or from one of the
machines?

I had a look through all 200 questions on the FAQ on the Transport for
London website, but couldn't find anything which answered my question!