Watch the Banjo 3 online guitar lesson by Joe Dalton from 50 Country Guitar Licks You MUST Know
G is not the only key we can use the open strings for in standard banjo sounds. I havn't played too much bluegrass in the key of E, but I have been able to interject some banjo rolls in other keys in various country grooves. There is a pretty wild banjo imitation solo in the key of E on Truefire's 100 Twangs Thangs You Must Know. It's definetly worth checking out.