The Ramban explains the function of the gold calf, that it was not meant to be an object of deification. The people were saying that the spiritual powers of this calf-like image brought them through the wilderness. This means the spiritual power associated with the image-the attribute of strict justice-and not the image itself.
My suggestion, based on this, is that Eileh is referring to those spiritual powers, ie plural
Actually, I've now noticed that earlier in in the parsha in posuk alef, it says Asay lonu elohim asher yeilchu... and Rashi says Elohus harbay ivu lohem - they desired to have many