bitcoind. Look at e. g. -rpcconnect=. (I haven't actually tried this.)
Ok, if it's possible good to know. However having bitcoin-qt or any other software with a GUI doing the same would be useful.
Just use the tools that are there. Tunnel with ssh if you really need this. Something like
"ssh -NL localhost:6666:your.machine.with.bitcoind.you.want.to.talk.to:8332
your.user@your.machine.with.bitcoind.you.want.to.talk.to"
and then run "bitcoin-qt -rpcport=6666 -rpcuser=whatever.on.your.machine.with.bitcoind.you.want.to.talk.to -rpcpassword=xxx.on.your.machine.with.bitcoind.you.want.to.talk.to"
Again, I haven't tried this (with bitcoin-qt). I have tunnelled with ssh.