war boost prolonged

“The boosts will initially be active for five days but can be prolonged use alliance gold (or by winning more alliance wars).” from the wiki

I have read somewhere that if you prolong a war boost until the end of the war and you achieve the same end result the war boost is prolonged free until the next war. So for example, if you finished the last war 3th you got the boosted gate. If you prolong this boost until the end of the upcoming war and you finish 3th or better the boosted gate is prolonged for free until the war after that.

My question: is this true?