How can I share a geth service and corresponding chaindata between multiple users but not a keystore / wallet?

Question

I would like to avoid storing redundant chaindata on the same system (MacOS). As per Ismael, it looks like a solution would be to run geth as a service and have both user accounts' Mist clients connect to that geth instance. I am able to start the geth instance and connect to it from both user accounts (with the help of knocte's answer here, but I cannot figure out how to do this while allowing use of separate keystores for each of these user accounts.

If I start geth using this command, a new keystore is created in the datadir, which is used by both user accounts:

geth --datadir "/Users/Shared/Ethereum/"

If I start it with this command, both user accounts use the specified keystore:

geth --datadir "/Users/Shared/Ethereum/" --keystore "/Users/[username]/Library/Ethereum/keystore/"

My goal is to allow multiple users to share the same chaindata and ideally run one geth service that can be shared between any user accounts on the same system. I'm open to suggestions if I am going about this the wrong way and there is a better way to acheive what I am trying to do.