While the addition of protein to the drink mix may increase insulin levels in the blood to help speed glucose transport across the cell-membranes into the muscles, that is not the limiting step to cycling performance. What does limit how many calories/hr you absorb is actually transporting that stuff out of your intestines. And that's a limited 200-250 cal/hr with a 6-8% glucose solution. More molality than that will result in slower gastric emptying and the stuff won't even reach the intestines fast enough. Lower concentrations than that will have less glucose touching the intestinal walls and limit how many calories/hr can be absorbed.
However, if you're doing a sub-maximal ride like a century or double, the protein and other solid foods eaten will leave your stomach feeling more satiated and calm. Won't do much for performance though.
BTW, ingested protein isn't used for energy in any way during exercise. Protein is only used when glycogen is depleted and this protein comes from the catabolism of existing muscle tissue. The ingested protein only goes towards repairing this damage later during recovery.