As you pointed out sensors push updates to the hub when they have data to report and sleep the rest of the time. So they’re no way to wake up a sensor and get the latest temperature.
You may need to try a different sensor which reports temperature updates more frequently and higher sensitivity.
For example you could use the Monoprice 4-in-1 sensor or the ZooZ 4-in-1 sensor which report temperate changes in smaller increments.
It could also be an issue with the mesh where the messages are being lost from time to time (common with sleepy devices). It would help to add a buffering device within 20ft of your sensor so that the updates are delivered more reliably. FAQ: why would I need another beaming repeater if my zwave lock is already close to my hub?