There are apps that will let you play your offline google music in other players. The one I use is Cloud music sniper. The free version only does like 50 songs, but I think to pay its only 2 bucks. It's not the perfect solution, but works well. One of the pay for players, can't remember if it was player pro or poweramp had it on the slate to bake that in, but I'm not sure they have yet.