Greetings,
This would not be a support configuration option on the MX since the general idea is that we treat VPN endpoints as point-to-point connections so anything outside of that, we cannot route to.
Another example is there you cannot forward traffic from an auto-VPN spoke, to a non-Meraki VPN peer.
Having said that, there might be some options here. If you cannot send it to the spoke MX public IP and forward it from there, then maybe we can use a proxy or another L3 switch/device that has its routable SVI in the local subnet of the MX, and the MX can ARP and port forward / NAT to that IP. The L3 switch/device must then send the traffic to the server across the spoke and that should work since from the MX's perspective, that's local traffic that can be routed.
Please let us know if you have any questions, and please don't hesitate to contact support if you need assistance in setting and testing this.