Perhaps Channel Express might be using a 737QC ex Belfast at night on one of the new postal contracts and then Jet2 using it during the day in pax config on some new services from BFS.
There are no night freight contracts to be had from LBA (too close to EMA for Royal Mail) and it could simply be planning to operate the Jet2 Leeds-Belfast schedule in reverse using a Belfast-based aircraft. It gets one more aircraft into the loop for a night contract without positioning and would also explain why the Belfast schedule hasn't gone on sale for Summer 2004 when most other routes have.
There were also some strange extra slot applications at Spanish airports for Summer 2004. They applied for an extra "Leeds" - Alicante on Fri + Sun (LS305/306) in addition to the core daily Leeds flight, an extra "Leeds" - Malaga on Wed (LS303/304) in addition to the core two daily Leeds flights and an extra "Leeds" - Palma on Tue/Thu/Sat (LS301/302) in addition to the existing daily.
Anyone care to place a bet that those extra Leeds flights (with flight numbers 3xx instead of 2xx) are actually going to be operated from Belfast in addition to the Leeds-Belfast service?