1) Create a host behind proxy
2) Create 'icmpping' on this host with a low update frequency for example '1h'
3) Create Calculated item which is using formula 'last("icmpping")'. Update interval 15s.
If calculated item will try to execute first. It will go to an unsupported state (because no data in the "input item"). Calculated item will never go out from unsupported state.
Attaching template for faster reproducing: