Perhaps making a small bash script that cds into the system-wide bb.edn project and then calls bb from there might be easier.
In /usr/local/bin or whatever dir is on the path:
/usr/local/bin/bbsys:
#!/usr/bin/env bash
cd $(dirname $0)
bb $@
/usr/local/bin/bb.edn:
{:deps {medley/medley {:mvn/version "1.3.0"}}
:tasks {:requires ([medley.core :as medley])
a (prn (medley/index-by :id [{:id 1} {:id 2}]))}}
Then from anywhere:
$ bbsys a
{1 {:id 1}, 2 {:id 2}}