When I have been issued a block clearance I use the phrase in the block FL430-490 and don’t refer to my current altitude. I don’t really know if that’s exactly right but I copied it from an American pilot I flew with (super bloke even though he later voted for Trump) and it seems to work. I have only ever been given block altitudes in European airspace by military controllers when conducting air tests, never for enroute.
I would like to add that American beer is not so bad that I refuse to drink it - I would simply like to find a pint of Hobgoblin or Bishops Finger in a bar in downtown LA one night. It would make me happy..