Would intravenous insulin + glucose significantly accelerate glycogen synthesis?
Concluding from this 1991 PubMed article, intravenous (or subcutaneous) insulin may not stimulate glycogen synthesis more than naturally secreted insulin.


  Experiments carried out in man have suggested that insulin may play
  only a permissive role in the determination of splanchnic glucose
  uptake. In a study by DeFronzo et al. (5), in which the plasma glucose
  and insulin levels were raised via peripheral intravenous infusion to
  223 mg/dl and 55 μU/ml, respectively, net splanchnic glucose
  uptake was 1.0 mg/kg per min. The rate of glucose uptake did not
  change appreciably when the arterial insulin level was raised further
  to 191 μU/ml.


So, at insulin level 191 μU/ml, there was no greater hepatic glucose uptake than at 55 μU/ml and hence no further stimulation of glycogen synthesis.

According to Emedicine, insulin levels can increase to 276 μU/ml 1 hour after glucose administration.

Which means that even naturally secreted insulin can reach levels that no longer stimulate glycogen synthesis and there is no point to give insulin by injection to stimulate it.