Right now we have an almost hidden feature that

1. ~/.sos/bin would be before anything
2. -b PATH would be preprended to $PATH.

This was designed to specify which command to use when there are multiple versions, but it would be a lot less flexible and useful to do

sos run workflow -b /path/to/R3.3

than

sos run -r host_p1

when host_r3.3 is defined with

module load R/3.3
sos run ....

since module load can do a lot more than setting $PATH.