Thinking a bit laterally perhaps..but...
Clear some space in the bottom of the overhanging cupboard.
Drill a neat hole in the cupboard base.
Funnel + pipe down through the hole into water tank when needed.
Fill funnel inside cupboard.
If you can arrange it so the pipe could be in situ permanently (i.e. are able to keep the pipe permanently into the tank), you could arrange something a bit more sophisticated than a funnel. Some kind of reservoir perhaps. Would not need to be large or take up much space.
If you move house, the hole can easily be closed with a suitable size grommet and look neat.
Anyway - not nearly as drastic as the holes in my kitchen worktop for full plumbing in ! If I move I shall use them as a selling feature "ready for your espresso machine"
As an alternative, when I had an Isomac Tea, I used a plastic cereal container with a plastic pipe going from the bottom of the container, through the top, down the side, into a hole (pre-manufactured) in the bottom of the Tea, up the side of the water tank then over the top and into the bottom of the tank. Established a syphon, and then just topped up the cereal container (which was more convenient than shifting the machine). Needed to be kept clean of course, but no more often than you should take the tank out of the espresso machine anyway. Has the advantage too that you can see the water level in the tank (as it will be the same as in the container). Used some plastic 90 degree pipe connectors to go round the corners to avoid pinching the pipe and keep it fairly neat. You might be able to find something a little more stylish than a cereal container if it's going to be on show.