AFAIK some Cisco devices support NOS tunnels wich allow multiple endpoints. But for IPIP on Mikrotik this approach means at the moment 366 individual tunnel interfaces since it accepts only PtP tunnels.
For IPIP, maybe some cheap standardized tunneling device, e.g. a Raspberry Pi with a specific AMPR image would be helpful, to accept IPIP encap traffic and ensure proper routing like below
| Pi tunnel endpoints | <---IPIP/RIP----> | Router | <---------> <Internet>