you TELL them you are setting off for the alternate. It is called 'command'. Safety comes first, ATC later. Their job is to provide the service.
Thats apparently the answer to this (which was completely rethoric):
Unless you know of a way (not involving a pan or mayday) to force ATC to let you fly the company planned diversion route
Seems to me your only interest is slinging insults at people, learn to read!
Btw telling them that you are diverting doesn't guarentee you will fly the
planned diversion route. They will sequence you with all the other diverting traffic! They won't guarentee an overoptimistic fuel planning towards that alternate.
So you will need to declare a Mayday to guarentee that the fuel planning works. What if everybody does exactly that? How is ATC supposed to sequence 10 mayday aircraft all about to land with less then final reserve.
Care to add a little to your (empty) profile?
To what end? As if retired, ATPL and UK tells me anything about you... might as well have made it up.
Saying random stuff like "its called, command" when nothing was asked in a rethoric question and not displaying any ability to make connections between various posts or recognizing sarcasm tells me a lot more about you. As do comments regarding me taking responsibility for others people's posts or even the dutch tv show.
If anybody is a bit short of marbles, it's you i'm afraid.