Unfortunately, I am quite sure it is not possible, but either way, the definitive answer should be set by our root admins.
This support request is being escalated to our root admins.
Edit:
As an alternative, you could request a free eu.org "domain" at https://nic.eu.org/. They do take a while to approve domain requests (all process is manually verified by a person) but it will effectively give you an address that you can host its DNS anywhere[1] you want and use it on your HelioHost account as well. E.g. https://kairion.eu.org/.
[1] I would recommend Cloudflare, Hurricane Electric Hosted DNS, or deSEC.