Change tempdir() in session (update R_TempDir)

Update: Simon Urbanecks unixtools package has a function to accomplish this. Below the code (for future reference).

set.tempdir <- function(path) {
  invisible(.Call(C_setTempDir, path.expand(path)))
}

C code:

#include <string.h>
#include <Rinternals.h>
#include <Rembedded.h>

SEXP C_setTempDir(SEXP sName) {
    if (TYPEOF(sName) != STRSXP || LENGTH(sName) != 1)
    Rf_error("invalid path");
    R_TempDir = strdup(CHAR(STRING_ELT(sName, 0)));
    return sName;
}