Can someone help me find a way to extend wonder timer?

Long story short: Me and my friends are casual players, and we never play rush and alway use a 35min treaty.

So we basically always play endgame stuff, and alway use wonders. We actually really enjoy wonder defense and invading well defended wonders.

But 300 years (or 400 with huns) is too short. Because wonders are not meant to be played with a no rush/35 min treaty. We want to change the wonder timer to at least 600 years, or 1000. So everyone can have a real shot at giving it all while playing such games.

As I said, we are very casual players and enjoy such games, rush and no treaty is not really the style of us plebs.

Is there a way to change that?