I've found a workaround for this problem.
Instead of using Qt main window, i've created a simple WinAPI borderless window, like in this SO discussion. Then i added QWinWidget from QtWinMigrate project, and filled window with it.
As result, main window and resizable edges are handled by WinAPI, and everything inside main window is handled by QWinWidget. And with QWinWidget you can create Qt gui like in any other Qt app.