I have played a little with this using SAS 9.4m5, not sure if there are any changes from 9.4m4.
Basically I was experimenting with just storing PROC S3 format configuration files in users home directories. For each bucket they need to access have them create a file text file in the .ssh directory with the name of the bucket can content like:
ssl=yes
keyID=key1
secret=key2
region=useast
Then they can do something like:
* Copy file to S3 ;
%let bucket=mybucket;
proc s3 config="~/.ssh/&bucket";
put "myfile" "/&bucket/myfile";
run;