Big starter question

I'm using a Wyeast smack pack and brewing up a 5 G batch of 1.117 OG barleywine.
I only have a 2L flask and stir plate for a starter.
I need some help stepping this up.
Mr Malty tells me i need 405 Billion cells.
I'll do a 2L with 1 smack pack, decant it...but then I'm lost on how much more is needed to further grow that up in the same 2L flask.

Appreciate any tips.

 

http://yeastcalc.com/
Use this.

It looks like after a 2L starter with a stirplate you could get the right cell ct with a 1L starter.

 

You could do a split step.
Make a 1.5L starter. Split that in half. Make another 1.5L starter with half the yeast from the original starter. Save that yeast.
Make another 1.5L starter, add the half of the original yeast to that.
That should give you plenty of healthy yeast.