FYI - I think everyone who has commented here is just trying to be helpful. Many owners may not realize the inherent dangers of adding a stick-on button. Sounds like you do and you are OK with it... so that is cool too.
While I'm not trying to convince you otherwise, I want to clarify the quote above for any future readers of this thread. Removing the airbag/horn assembly is downright trivial. There are only two screws to remove it. They are under round-ish plastic plugs on the back of the steering wheel. Use a 1/4" ratchet with a deepwell 6mm socket and you can have them out in two minutes. The horn/airbag assembly will now flop forward exposing the two airbag connectors. Before disconnecting them, touch the bolt securing the steering wheel with your fingers. This will insure that you have discharged any static electricity. Now you can remove the airbag connectors. With the assembly out on a workbench and facedown on some soft cloths, once again touch some nearby metal surfaces to make sure you are statically discharged. You can then remove the 4 small nuts securing the small airbag module to the horn module. With that removed, you can now safely (and legally) ship the horn module off for repair. Assembly is just the reverse order. Just take some precautions that you are statically discharged before handling the airbag module or its connectors.