Sounds like a plan to me.
I never said put 3.5 liters in a 2 liter vessel. Just reporting the facts from Mr malty. If you can figure it out then great, if not then wait.
Not sure if a stir plate will work with a carboy though but I applaud the out of box thinking!
If you have a stir plate and 1 yeast pack based on your original numbers you should do a starter of 3.54 liters or 1.73. According to Mr Malty. I would think 2 days would be enough as long as your ok with not cold crashing and decanting but instead just throw the thing in like some people do at...