OK, I wrote my own:
function IsMousePointerOverIEVBitmap(AIEV: imageenview.TImageEnView): Boolean;
var
p: TPoint;
begin
GetCursorPos(p);
p := AIEV.ScreenToClient(p);
p.X := AIEV.XScr2Bmp(p.X);
p.Y := AIEV.YScr2Bmp(p.Y);
Result := (p.X >= 0) and (p.X < AIEV.Bitmap.Width) and (p.Y >= 0) and (p.Y < AIEV.Bitmap.Height);
end;