Not done it myself but had my clutch on my S3 replaced a few years back. You can do it in situ, some mechanics can do it by just dropping the front sub-frame which will take about 4hrs labour; others will take almost double that as they remove more bits and bobs to get access (and it's an 8hr job in Audi dealers eyes). Oh, and you should really have the alignment done once the sub-frame is back in place.
When I was pricing it up I had JBS quoting me 4hrs and The Phirm quoting me 8 hours. JBS did the work and 4+ years on not had any problems.