Well, I decided the way to get the boxes at work to handle the new DST is to create a new timezone.
This is what I used:
# Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule US 1967 2006 - Oct lastSun 2:00 0 S Rule US 1987 2006 - Apr Sun>=1 2:00 1:00 D Rule US 2007 max - Mar Sun>=8 2:00 1:00 D Rule US 2007 max - Nov Sun<=7 2:00 1:00 S # Zone NAME GMTOFF RULES/SAVE FORMAT [UNTIL] Zone US/Central-New -6:00 US C%sT
The pre-2007 part is lifted from an old tzdata source file, and is just so that the system will know that DST isn't in effect yet.
Now fingers crossed, these old production servers will have the correct time in March....