I've also thought of that possibility as BMW is famous for having a cover wtih a gasket that seals all the plugs/COPs water tight as well as having a seal around each COP using the seal shown in my attachement.
It seems like a better use of time to theorize a better seal for the COP. Me personally, I use dielectric grease on the top lip of the COP where it meets the head. Haven't had a problem yet, but I don't drive like the OP I don't think lol
I have also thought of this. Tried creating an 'umbrella' of sorts using silicone sheeting however, can't seem to find one thick enough without having to buy it in bulk.
Have also looked into using a spark plug tube seal from a BMW or 300Z but the sizing is the limitation. Looking for a manufacturer that has a large aftermarket assortment that they manufacture so they can match the spec size I would need. (Pictured)
I am also looking into simply replacing my ignition system to delete the COP's and replace with good ol' fashioned plug wires as many are made with a seal at the end that POSITIVELY seals the tube closed. It would take some re-wiring and synchronization but is possible.
although expensive.