Tom, you are correct in saying that dildoes is an alternate spelling of the plural of dildo. The problem is that dildoe is also an alternate spelling of the singular word, and is acceptable, as a rare word, in Chihuahua. Hence, dildoes is ruled out as the plural of dildoe.
The singular version with the e is quite rare, though Google Book Search returned me 1460 hits on that spelling. But since the plural spelling with the e is also rarely used, I don't think I should insert dildoes, so to speak.
One usage, for which both spellings are employed, is for a plant, the dildo(e) tree. In the words of the Shorter Oxford, "Any of several W. Indian cacti with tall ribbed cylindrical stems..."