> it doesn't really make sense to incorporate in US if then I will run the company from abroad its entire lifetime.

What made you think that?

> Is it possible to avoid incorporating in US if accepted in YC?

No, it's not possible. From http://www.ycombinator.com/apply/

"International founders, please note: if your company is a non-United States entity (corporation, limited liability company, etc.), your participation in YC is conditional on conversion of your foreign company into a United States corporation."