Answer:
You can't, because the SSJ5 level hasn't been officially created by Akira Toriyama (the creator of Dragon Ball).
But if you really want to play against a SSJ5 Goku, you can search for a hack of Budokai 3 (NOT Budokai Tenkaichi 3, notice that) named Dragon Ball AF.
First answer by ArkBlitz. Last edit by ArkBlitz. Contributor trust: 0 [recommend contributor recommended]. Question popularity: 2 [recommend question].