In winGRASS 7 (download standalone installer) the Windows batchfiles for use with R (https://code.google.com/p/batchfiles/) are now integrated for a smooth GRASS-R-coupling in MS-Windows. For the usage see here:
https://grass.osgeo.org/wiki/R_statistics#Usage_III

Note that this integration is available for Linux users for a long time, however, finally also the winGRASS user can enjoy this integration!

Thanks to Helmut Kudrnovsky from the GRASS GIS team and to the Windows batchfiles for use with R team.