APPROVAL PENDING
Since you seem a little doubtful about this, perhaps instead of "removing" the Innocence the gas make it move. As you mentioned, the Innocence is in his blood, so maybe it could be moved to just being in his blood instead of in his arm? He would look completely normal, but the Innocence would still be inside of him (and he might not even realize it, but it's similar to when it hid out inside his heart?). I'm not sure if this is a compromise like you would want, but it might lessen the needed damage control?
And the idea of the curse getting angry and activating/unactivating at random could be interesting. Especially since Allen may end up seeing souls of people randomly as well.