SORRY for the mess, I've already figured it out myself, wish there could be "Delete thread" option for the author...
So, at least I'll post my solution if anyone comes at a similar problem:
#define WM_LACEWING (WM_APP + 1)
void onTickNeeded(Lacewing::EventPump &EventPump)
PostMessage(FindWindow("WindowClassName", "WindowName"), WM_LACEWING, NULL, NULL);
//In your WndProc loop add:
case WM_LACEWING: EventPump.Tick();