Hello,
The R&S RTA4000 makes it possible. With Agilent DSO6104L and the Rigol DHO1074 I couldn't manage it. Of course it doesn't work with USB devices either.
If I remember correctly, it works with the Rigol DS1054z and the Siglent SDS2104X Plus.
Best regards
egonotto
P.S.: It's strange that it's exactly 50,00000 Hz, I've never measured that here before.