When attempting to freeze a track that has sidechain routing in it instead of displaying an error message Live should provide an option to freeze up to the sidechain and keep the devices past that point active. i.e. partial freezing.
Example track:
Synth | Delay | Autopan | Compressor (sidechained) | Filter | Reverb
In this case Live would Freeze the synth, delay and autopan and leave the compressor, filter and reverb active still on the track.
To do this manually you need to put the track in a group and put the unfrozen devices in the group. This only works if the track isn't already grouped. Alternatively you could create a new track, set it to monitor in, rout the audio, replicate any sends and automation, etc. This isn't difficult to do but it is very disruptive and annoying workflow-wise and makes it inconvenient to freeze and unfreeze many tracks multiple times. Also, it makes sets quite messy with duplicate tracks or groups everywhere.
It'd be much better if tracks could be partially frozen in the manner described above.