You used to be able to get a radiator valve that had valve and lockshield combined that had a tube that extended into the radiator. We had one on a radiator in the last house but I have not seen one for years now, certainly not from the usual suspects, a good plumbers merchant might have some stock. Whether it will actually save you some space, I don't know? If the plan was to have a TRV then you will not get one with this sort of valve. Other options to explore are radiator adaptors plenty of extending ones about if you can get an angled one you should be able to tuck the valves below the radiator as an angled adaptor would probably occupy less space than a valve.

Richard