The most likely fate of excess CHO is glycogen, which is a large polymer of usually glucose or galactose. These polymers can accumulate, but aren’t fat per se. Some metabolites, such as pyruvate (the end product of glycolysis), to name one, can be shunted into just about any metabolic pathway including fatty acid and amino acid synthesis. The connection is not very direct, though. You have to process the CHO to a metabolite like pyruvate which can enter the pools of central metabolism and from there it can go almost anywhere.
I’m not sure if this is exactlyl what you are trying to get at. Sometimes an excess of CHO can lead to abberant accumulation of products, like ketone bodies in diabetic ketoacidosis, for instance, but these kinds of things are often a reflection of the inability of normal pathways to handle the extra flux demanded, and so metabolites accumulate. Accumulated metabolites may be toxic, so the body tries to do something with them, if it can, to reduce the metabolic stress.