You need to not be so nice about it. You say you don't want to get him in trouble, but that YOU are getting in trouble.
If he is doing a piss poor job of loading (his job) then he needs to be retaught, or canned...or as UPS goes promoted (when you suck at something, we'll just push you further up the ladder).
I'm a cover driver, and there is a loader that loads 2 of the routes that I often run and whenever he does, he is HORRIBLE. Once he put 2 over 70's on the top shelf, while the smalls sat on the floor
And I have gone to his boss before, and nothing changed. He loaded my truck yesterday and I puled an 11 hour day, as opposed to the SAME route when loaded by the loader who used to do it I tear up in under 9 hours.
Your best bet, however is to talk to the guy and try to refrain from using the following words: Stupid, Incompetent, retarded, illiterate, Dumb. SOMEtimes, talking to them and asking them to put things n certain spots, will work. Now, they usually can't figure out EVERYTHING, but hey...baby steps. HAHA