mikeyrf So far all of the wallets that have integrated with it have listened to the actual transactions via horizon (since transactions don't necessarily have to originate from the wallet anyway).
However, adding a callback was one of the things that was on my list of things to do. If doing that now would be helpful to the integration I can add it for the next release (likely Sunday evening, but I could do a special release for just this if it is time sensitive on your end).