Making yeast last

I want to make Duvel. The recipe I have says to pitch yeast twice. Ferment once for 7 days and then rack to secondary and pitch yeast again. My question is: can I just buy one bottle and make it last? I'm thinking use half of the original yeast, make a starter a few days before saving the other half and then making a starter with the second half a few days before I pitch the yeast for the second time.

My follow-up question would be: if I can get away with this why not do it all the time and use 1 vial for every 2 batches?

better way is to make starter and pitch into a batch. then when it is done, wash yeast in 6 (1 pint) mason jars...use each of these like the original and don't go beyond 3 generations... that gives you 6 x 6 (or 36 batches) from one vial w/ little work.

outstanding pictorial on how to do this. taught me how

https://www.homebrewtalk.com/f163/yeast-washing-illustrated-41768/

I think it's odd the recipe is calling for pitching the same yeasts again in the secondary.