I would also recommend that you brush up on Mass & Balance; something like re-learning the usual definitions like MZFW, MTOW, MLW, RTOW, traffic load, underload, ramp fuel, Take-Off fuel, trip fuel, etc. and knowing the relations between them will pay dividends when you are let out on your own to turn around a lo-cost 737 in 25 minutes flat!
The CAA yellow booklet provided for the frozen ATPL exams should be sufficient in that respect, but you can also use whatever feedback or ATPL groundschool material you still have. Brushing up on performance can be useful too.
Once at the interview, be modest and don't overdo the "I've got a frozen ATPL, so I'll be fine as a Flight Dispatcher" thing; it might just upset your interviewer...
G'd luck!
