Any tips for dealing with hyperglycemia during chemotherapy?

My grandfather has lung cancer and is doing 32 doses of radiation (once a day) and "light" chemo once a week. Today he went in for his second day of chemo and his doc said his blood sugar was very high (300). I did some research and found that chemo can cause high blood sugar.

Any tips for dealing with this? We've found some cursory tips like drinking more water and eating less sugar (obviously) but I'm sure the wonderful people of reddit can give us some more info :)