More complicated things to do: may require investigation or acquisition of new kit.
Track cleaning train schedule. or schedule sequence.
Consider splitting one or two platforms at Portsmouth to allow two shorter trains to use them. A bit like the shorter blocks in the fiddle yard. Trains would need to arrive at the 1st block, and a "move down" schedule would be needed. A lot of schedules would need to be edited! BDL169 #30 has 5 spare detection sections, including all of Zone D; so sensors are available.