It is certainly possible to gain a PhD in Germany with minimal contact with the supervisor assuming you don't need access to any equipment. What I would question from the experience of friends who did just that, is whether it's worth it. The two people I know got nothing career wise from it, just the title. It seems that if you are not involved in the day-to-day activities of the 'Lehrstuhl' (I have no idea what this is in English sorry - there's no real equivalent), then you are very unlikely to benefit from the professor's patronage, which is crucial for getting academic jobs in Germany in my social science field at least. So maybe the question is why do you want to do a PhD?