Yep I was looking at that option too: it'd give me about 400bn cells I think. Actually my batch size is 32 litres though, so I think I might try to get a bit nearer 600bn.To be honest if I was doing a 23l batch and was stuck with a 2l flask and the pack of yeast that you have then I'd just do a 0.8 litre first stage starter, chill, decant, add a 1.4 second stage and call it close enough. 1.5 litres of lager yeast in a 2 litre flask shouldn't overflow.
I'll probably start with a 1 litre volume and see how much it froths up...