[Users] outer boundary conditions

I am wondering what existing support there is in the einsteintoolkit for outer boundary conditions appropriate to cosmological problems? I do not seem to find anything directly relevant, so please let me know if I have missed something. Suppose one has a given interior problem which uses spatially asymptotically flat boundary conditions for all variables. Given that I was wondering how hard it would be to redo the problem replacing the asymptotically flat with asymptotically expanding at the edge of the spatial mesh?

Thanks for any help.

Comer