Hi Dirk:
Unfortunately MK20DX256VLH7 is not supported in MCUXpresso SDK. There is no guider or work around to port it from an existing SDK.
If you use the other similar SDK to run the specified chips, it is possibly that you may encounter issues because there maybe difference between IPs IN 100M and 72M. And NXP support can't help on this.
You can download the bare metal code examples from below link
TWR-K20D72M|Tower System Board|Kinetis MCUs|NXP
Or you can use Classic MQX 4.2 (free) , TWR-K20D72M is supported.
Regards
Daniel