I don't really see the point, it would be a lot of work and you'd struggle for space, not just for the two turbos but all the pipework that would be involved. A K03 from a 1.8 20vT passat spools up as fast as you could want, next to no lag.
If you were going to do it then sequential turbos would be more interesting. That is one small turbo to produce boost low down the rev range and then a bigger one which start making boost as the small one is reaching it's max flow. But again, it's going to be a hell of a lot of work for little gains. Yet another option is using a bigger turbo and nitrous off boost to overcome the lag.