All the threads I've read on the subject agree that you can use Enlarge Person on an Eidolon
http://paizo.com/threads/rzs2pugr?Share-Spell#1
http://paizo.com/threads/rzs2mf3f?2-summoner-questions#1
http://paizo.com/threads/rzs2mwq7?Summoner-and-Eidolon-Errata-and-Questions #1
http://paizo.com/threads/rzs2mqmx?Enlarge-Person-on-my-Eidolon#1
http://paizo.com/threads/rzs2m9yz?Eidolons-and-Enlarge-Person#1
http://paizo.com/threads/rzs2lkcc?summoner-spell-question#1
but my question is, is the spell restricted to a humanoid-shaped Eidolon or can other body forms benefit from it?
Spell description states:-
"This spell causes instant growth of a HUMANOID creature, doubling its height and multiplying its weight by 8. (etc)
A HUMANOID creature whose size increases to Large has a space of 10 feet and a natural reach of 10 feet. This spell does not change the target's speed"
Does the Eidolon exception to the normal Enlarge Person target requirements stretch as far as non-humanoid body types?
Cheers,
G.