We just came back from D-camp and the doctor, who has several decades of T1D under her belt, told us that she basically just keeps glucagon unrefrigerated and uses it in mini-doses until it stops working, which is often weeks!
That sounded risky with kids but on the other hand, in our experience mini-gluc works faster than eating a snack, so if it's potency is reduced, for mild lows you still have time to use food or increase the dose if it's not sufficient.
Another kid there experimented with putting glucagon in one pump and insulin in another. She found it worked great to give herself minidoses that way, but that it worked with decreasing potency when kept against her body. She said that wasn't a problem though; when it stopped working, she just increased the dose slightly.