You can directly reference the image url in a reader, but it is going to ‘download’ it regardless, in this case, store it in a temporary location.

It’s also going to be quite a bit slower to read in the data than it would if you were accessing a file on your local machine

I guess if you store your rasters in a database format you could run SQL to get the pixel value for a known point and let the database do the work for you.

For PostGIS ST_Value() would be your choice for a SQL function.