It's a bit of a fudge, but I can't find a better way of doing it!

Set the TRV to full (preferably replace, so the radiator is lockshield both
ends). Then balance down the hall radiator using the lockshield so that it
warms up slowly and doesn't get very hot. Then, when the other radiators get
shut down via their TRVs, more water gets to the hall radiator. By the time
all TRVs have shut, the hall radiator gets the full force of the boiler,
heats the hall and the room stat shuts down.

I suppose you might argue that that we might as well set the stat to
45C in the evenings and let the TRVs do their job,

This would defeat the boiler interlock and make your system inefficient, as
the boiler will continue to short cycle, heating your primary water which
may lose heat into areas not required to be heated.

Christian.