BOH - I suggested not so much to compete with LGW, but just to get some of the South East market. Probably a BFS/NCL sized base. Jet2 is an unknown brand in the SE, and even those that know the name don't know what they're like to fly with.
The airport has ILS on both runways including CAT3A on one end. It doesn't have a parallel taxiway in the "normal" sense, but aircraft can taxi in and out without getting in each others way. Night closure from 9:30L is probably the biggest barrier, but given some thought as to the scheduling could work - i.e. an aircraft couldn't do 2 long flights per day, but 1 long and 1 short/medium could work. E.g. TFS and DLM wouldn't work, but TFS & ALC and PMI & DLM would.
LPL - that may be a large part of their market, but they also serve the typical routes Jet2 does. Every passenger that flies to Spain/Greece/Turkey from LPL with easyJet is a passenger Jet2 could have.
My point about MAN wasn't so much about capacity but what markets are left open to Jet2? Besides Morocco, Egypt and maybe Cape Verde, which even serving all 3 would only use 1 or 2 aircraft, what new destinations are there? Besides being Airbus instead of Boeing, what will the Jet2 MAN base look like in 10 years time?