Hello @Rayn ,
between two routers you could use L2TPv3 that provides a point to point L2 transport service.
With 5 devices connected via DMVPN I think it is a problem to create such emulated broadcast domain.
You could use an MPLS service provider service like VPLS and using simple switches as L2 CE devices in this way you would avoid to overload your routers and that service would run in parallel with your DMVPN.
Hope to help
Giuseppe
