How to make a 4 quart starter?

So, I need to make a 4 quart starter. I have 1 vial of WLP 029. My starter flask holds 2 quarts. In order to save myself the $7.00 for another vial of yeast can I just totally ferment my first starter, let it settle, decant the wort. Then boil another starter wort and add it to the yeast cake left over from the first starter, and let that ferment out and pitch that second yeast slurry into my 5.5 gallon batch?

Is that how you guys do it?

Yes you can do that, but I don't think you'll reach your optimum cell count, simply because you will still only have a 2 qt container. Ideally you'd want to have a container larger than 4 qts and step up your starter to your desired size.

But what you have in mind would be the next best approach if you dont have a larger container. Or you could split it into two.

Use a gallon jug. Start with 2 quarts and then add 2 more quarts a day later.