Make up a "cover" for each of the new clerks, to be given to them without a lot of fuss, with nice stamps, a desirable cancel, notes written directly on the covers about the undesirability of spray cancels, why covers can't be bent, folded, or scuffed, why the collector on the other end will love the cover, etc., etc., etc. Be sure to use 4 or 5 old stamps, like 2x13c, 2x10c, well away from the edge of the envelope, where they frequently get damaged in the machine.
A visual guideline, so to speak, with every factor either illustrated on the cover or annotated in small inconspicuous letters, their "guide" to keep and learn from. Cost to you, less than $1 each.
Design a sample and post it on SCF, and we're bound to think of small improvements and features, then everyone can make them as needed. Address the cover to Obama, no one will forget that. Be sure the stamps are cancelled with "cancels" you have drawn on the cover, so it doesn't mistakenly get sent and then when you're not looking, they will appoint you Postmaster General, then you'll have to quit your day job.