Stratified spatially balanced random sample (GRTS) in R

I have grid (spatialpolygonsdataframe) that I want to draw a GRTS sample from across two strata. I have "treated" and "untreated" cells and I want to draw a sample of 25 from each. Does anyone know of an R function that can draw a stratified spatially balanced sample.

neither grts.polygon in SDraw or grtsarea in spsurvey seem to have this capability

Thanks