What im doing to practice agility is learning a peice then slowly increase the tempo untill its super fast, to get a hang of fast play. An organist told me playing scales will increase agility, so im doing that too. She also told me that playing Hannon is good for agility too, i think playing the Hannon excersises in all keys will help (i think, i would really try it though, i tried doing one of the excersises in G major and it really hurt).
Be warned though, she seemed to have carpol tunnel so im not sure its a good idea to follow these things, the playing Hannon thing at least.