How to use European subnet with US-based VPN tunnel

First of all I would like to explain that I am taking my first steps in networking in general and in GCP in particular.That's why I apologize if the question makes no sense.

I'm facing a challenge with routing traffic from a subnet in Europe through a VPN tunnel based in the United States.

Here are the specifics:

  • Subnet details: located in europe-west1, containing 2 instances
  • VPN tunnel: Set up in the US, with the Cloud VPN gateway in us-west
  • Issue: Cannot add the europe-west1 subnet to the tunnel due to regional differences

Current limitations:

  • Unable to modify the other side of the tunnel
  • Cannot relocate the Gateway to europe-west1 as it would result in losing the IP configured on the other side of the tunnel
  • Unable to select a different range of local IPs for the tunnel.
  • Cannot move the instances from europe-west1 to another region

Attempted solutions:

  • Verified routing tables
  • Tried creating a Cloud NAT between the two subnets, but this approach doesn't work as both subnets must be in the same region
  • Attempted VPC peering, which yielded the same result

Core question: Is there a method to route traffic from instances in one region (europe-west1) through a VPN tunnel configured in a different region (us-west)?

The only thing I can think of is to create another instance in a subnet in the US that acts as a proxy between the instances in Europe and the tunnel but it seems a very inefficient solution and I would like to know if there is an alternative that escapes me.