Procedure? Simple - find a different solution.
The calculator uses variables, and each variable changes starter volume. More than one vial, a stir plate, and fresher yeast would all bring the starter volume down to a more reasonable size.
4L is not a normal starter; it is more like a batch of beer. It is simply the result of plugging in many unfavorable variables.
I say look into a stir plate, because it dramatically reduces the volume of wort as well as the number of vials required for an appropriate cell count.
If $75 for the stir plate is too big a nut to crack, opt for a second (or third) vial, but in that case, the stir plate would have paid for itself in about a year of brewing.
Joe