In case anyone's interested, I had a go with some code using this method and it worked with only the specified bytes coming down the line.
However, with specific reference to OP's requirement, I've found that the EXIF portion of a JPEG file isn't a fixed length and for very large JPEGs can be larger than you expect... A few tests I ran (as I'm finding this thread particularly interesting...) showed that sometimes over 10K of download was needed before ExifTool would recognise the EXIF data...
fx, Infinity is Colourless