I disagree with Monica Cellio's answer because I think that a hefseik should be permitted in cases where there is no hesech hadaat. For example, the shehechiyanu blessing in Yontif Kiddush is recited after the borei p'ri hagafen but before the wine is drunk. So too here, we should be able to say e.g. regarding Crispix cereal that reciting two blessings one after the other is part of the nusach habrachot for that food and there is no hesech hadaat like kiddush on yontif.
(This hefseik is not unrelated to what you are doing. See Identitytheft-Dave's comment on the initial question.)