As a follow-up of this interesting question, I would like to take one step back. Most say Kaddish deRabanan after the morning Korbanot (see Emden), Ein kEloheinu and Bameh Madlikin. In contrast, Heidenheim seems to omit this kaddish at all three places. What are the earliest sources that mention this practice in a public prayer setting?
As I noted in a comment there, Tur OC 270 mentions a kaddish after bameh madlikin and Tur OC 133 in the name of Rav Amram Gaon mentions a kaddish after ein kelokeinu. (I would be extremely surprised if there is an earlier source than Rav Amram Gaon).
It should be noted (as was pointed out by @DoubleAA) that in both of these places, Tur only mentions kaddish generically, but does not talk specifically about kaddish derabbanan.