How can we add an R library path with TSSS


We're running TSSS v7.5 on a Red Hat EL 7.3 server.

We would like to install some third-party CRAN packages for use with Open Source R (not TERR).

When running R through TSSS I can see that the R library paths are:

/opt/TIBCO/statsvcs75/SplusServer/libraryCache/1/library   (owned by tsssuer)
/usr/local/lib64/R/library   (owned by root)
/opt/TIBCO/statsvcs75/SplusServer/library/R/3.0   (owned by tsssuser)

We would like to add a fourth directory to this set of paths into which we will install the third-party packages. Typically, this is done by setting R_LIBS_USER in /home/tsssuser/.Renviron but this doesn't appear to work. I've also tried appending R_LIBS_USER=... to /usr/local/lib64/R/etc/ but that doesn't work either. The R library paths are always the three listed above when R is run through TSSS.

How can we add a custom directory to the R library paths when R is run by tsssuser?