We are cleared to FL100. When at FL100 the controller requests us to take a radar heading 090 because of some traffic they want to slot around us. While on this radar heading we enter IMC. If I was VFR I would not be able to accept a radar heading that took me knowingly into IMC.
I think you need to understand the exemptions that parachute dropping operates under in CAS. You can either talk to the BPA or NATS.
As for the rest of your suggestion on logging, strikes me as a good compromise!!
Don't get me wrong, I understand fully the type of operational pressure you are working under especially in UK conditions where quite often you will be in IMC in very odd aircraft configurations waiting for the required hole to appear in front of you which will give the 'cargo' clear sight of the ground.
It may not be departure and arrival experience but it is sold instrument experience transition on and of the clocks a dozen or more times an hour.