CC-reduplication
Fragment of a discussion from User talk:Rua
The normal kind of reduplication only copies the first consonant. The consonant is s, the next consonant is also copied. This wouldn't give the Greek form, no, but I don't know what does.
Note that he also mentions *CeC- reduplication. That looks more like ἤγαγον (ḗgagon), but may not be quite identical in details of form or meaning. I'm going to see if I can find a description of the verb in Sihler, which I got ahold of finally.