Hi Hibbo,
I would go with your option 3, but before the power is disconnected, have a kettle ready boiled. As soon as the DNO guy pulls the fuse, shove a really hot cuppa in his hand. That should give you 10 minutes or so to rip out the old c/u before he is ready to fit the isolator.
If you are a slow/steady worker, i suggest that you get one of those insulated travel mugs for his cuppa, that'll give you an extra bit of time before the tea cools enough to drink it. Most folk in this sort of job would be quite compliant whilst they have tea in hand
it worked for me in the past, once had a nice long chat with a dno guy whilst we were both eating the customers biscuits (hob-nobs, mmmm yummy)