not possible 100% in RTW engine-if you are that picky, take 2 suggestions:
1-in RTW: use guard mode-that simulates it quite well. and charge the momet you see the men lock shields to meet the enemy (around 40-50m). when on impact and fighting, order them to attack again (with double click), on who they are fighting, that simulates the push. needs micrro managing, but no one said hoplte battles were simple to coordinate..
2-or switch to BI (that's easy enough), and play with the EDU...

otherwise-they are doing what they are told. the EB team has done its best to recreate hoplite warfare under the ridiculous circumstances..including the game engine and the overly nitpicky.
and as for the fella arguing that the hoplite doru use is wrong, 2 words: chigi vase. 2 more: Alexander sarcophagus. a few more: about every depiction of hoplite warfare in the timeperiod...

(look them up).
also having read medieval works, the "old fashioned use" of spears is described as the overarm type-indicating universal and very common usage (it was in a history written about the English fights with the welsh-the same one that discussed the poor knight who lost his horse with an arrow that went through his thigh and into the horse. you know what weapon that is). that's why 90% of all spear armed EB units use this method..