I continue to use eye drill, and if you are having trouble with the tangerine method you can try substituting it with the Einstein concentration drill - though it take's awhile to do it. It can last from anywhere from 6 weeks to 6 months of concentration - or so they say.
As for tangerine method - I find it easy to do as I was the worlds's greatest day dreamer growing up - still am to some degree.
As a suggestion, if you are having trouble imaging the feel, smell, tecture of the tangerine ... try puting a real one in your hand feeling for tecture, size, smell ... and do this until you can let your imagination take over.
Another thing I find that helps when applying the tangerine method is that 'anytime' during my photoreading session if I find I am losing concentration, I quickly image putting the tangerine behind my head ... should help to refocus.
Another thing, is to breath deeply. You may have to consciously do this for awhile but as with anything ... it will become a habit.