Thanks to a tip found online, I bought a PoE splitter / adapter,
in my case via https://www.bol.com/nl/p/12v-poe-spl...0000055254940/

This works well. Connected to a switch with PoE (15W is enough, PoE+/30W is not needed), this will power your Spark over utp, while retaining the network cable plug to send your data through.

Use this advice at your own discretion, I can not guarantee proper operation and/or lack of damages, these are all at your own responsibility.