On the subject of the magnetic uncouplers, I was experimenting with them again last night and managed to get the delayed uncoupling to work, albeit not 100% reliably.
I ended up removing 1 sleeper and placing 3 magnets, poles facing up, in a row. You won't get them right next to each other as they repel, but you just push them as close as possible.
I'll be working late so will have to post some pics later on.