I don't purge headspace when lagering, but the initial sulfur smell seems to go away with extended lagering/cold conditioning. It can't leave the system, so maybe it turns to sulfate anion somehow? I couldn't find anything in fix or noonan, or the thread about what happens during lagering for that matter.
As a side note, I'm just drinking a helles/dortmunder hybrid that has been kegged and conditioned for about 10 days. There's a bit of sulfur, but it might be a lot less noticeable if the beer was more bitter, pilsner style. In any case, the beer was pitched w munich lager wyeast, tons of it, when the wort was 49 or 50F. I f'd up putting ice in my cooler that pumps cold water into the ferm chamber on day 3 or so after pitching. Temp got up to 59 in the fridge, not sure about the beer. There was prob 18hrs of this ambient temp. Got it cooled down soon, and kept it at 50 for 2 weeks or so. Raised temp to 60, and left the beer on the primary yeast FOR 6 WEEKS! Got lazy I guess. In any case, this lager is going to turn out really well. So the initial bump didn't hurt, nor the extended time at 60, not the time on the primary cake. Just so everybody knows, it is possible to do what I did and make a great lager. It's going to be great when this sulfur goes away!