Yes its possible...I think
www.vickauto.com sells a hub adapter for Nardi wheels and there are also hub adapters for Momo steering wheels.
My airbag system does not work and I look at it as more of a liability myself so I have disconnected it to prevent (hopefully) a misfire at an inopportune point. I have purchased a beautiful wooden Nardi wheel and adapter but have not been able to remove my steering wheel. (basically stripped the stud holes with a puller....another project to complete someday)
If Alfa were still in the US, the airbag system would probably be just like any other system and servicable. Now the price to replace it all after the 10 year point and bring it up to snuff is prohibitive. Let alone documenting the work and possible liability when you sell the car to someone and the bag doesn't work during an accident?
In any case, I think those of us S4 Spider owners kind of walk the line of liability anyway with these old air bag systems no matter what you do with them. A good compromise if you really want to keep the air-bag wheel yet want the "wood-look", there are Miata (blashphemous, I know) shops that will refinish your wheel with leather and wood....the websites look pretty nice actually.
Anyone else have thoughts on this one?