[plt-scheme] environment variable for R6RS libraries?

I have read the docs about the R6RS support (http://docs.plt-
scheme.org/r6rs/index.html)
and it seems that there is no such a thing like an environment
variable for the search
path (like LARCENY_LIBPATH, IKARUS_LIBRARY_PATH, YPSILON_SITELIB,
MOSH_LOADPATH). Am I correct? Are there plan to add a PLT_LIBRARY_PATH
in the future? As of now I am putting symlinks in the collection
directory, but it is
rather inconvenient.