@caedmon - I think you best bet would be to use a BeastMode Calculation to do this.

It would look something like this - 

CASE
WHEN `Date Column' = January then 1
WHEN `Date Column' = Febuary then 2
WHEN `Date Column' = March then 3
WHEN `Date Column' = April then 4
WHEN `Date Column' = May then 5
WHEN `Date Column' = June then 6
WHEN `Date Column' = July then 7
WHEN `Date Column' = August then 8
WHEN `Date Column' = September then 9
WHEN `Date Column' = October then 10
WHEN `Date Column' = November then 11
WHEN `Date Column' = December then 12
ELSE 0
END

Then you would sort the BeastMode and everything would end up in order.

Now I'm no BeastMode expert, so the code above may not be perfect. I'd recommend checking out the BeastMode section - http://dojo.domo.com/t5/Beast-Mode-ETL-Dataflow/bd-p/Beast