$ export GNUPGHOME=/tmp/foo
$ gpgconf --list-dirs | grep agent-socket
agent-socket:/run/user/1000/gnupg/d.e4eiyium4hwx3rfwiz5r1won/S.gpg-agent
$ gpgconf --homedir=/tmp/bar --list-dirs | grep agent-socket
agent-socket:/run/user/1000/gnupg/d.chpsd6ko5dz3abqx9h317bj5/S.gpg-agent
$ gpgconf --homedir=/tmp/bar --create-socketdir
$ test -d /run/user/1000/gnupg/d.chpsd6ko5dz3abqx9h317bj5 ; echo $?
0
$ gpgconf --homedir=/tmp/bar --launch gpg-agent
gpgconf: error running '/usr/bin/gpg-connect-agent': exit status 1
gpgconf: error running '/usr/bin/gpg-connect-agent NOP': General error
$ strace -f -e trace=connect -- gpgconf --homedir=/tmp/bar --launch gpg-agent
strace: Process 27236 attached
[pid 27236] connect(3, {sa_family=AF_UNIX, sun_path="/run/user/1000/gnupg/d.e4eiyium4hwx3rfwiz5r1won/S.gpg-agent"}, 61) = -1 ENOENT (No such file or directory)
[pid 27236] +++ exited with 1 +++
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=27236, si_uid=1000, si_status=1, si_utime=0, si_stime=0} ---
gpgconf: error running '/usr/bin/gpg-connect-agent': exit status 1
gpgconf: error running '/usr/bin/gpg-connect-agent NOP': General error
+++ exited with 1 +++
$ gpg --version
gpg (GnuPG) 2.2.12
libgcrypt 1.8.4
Copyright (C) 2018 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <https://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Home: /tmp/foo
Supported algorithms:
Pubkey: RSA, ELG, DSA, ECDH, ECDSA, EDDSA
Cipher: IDEA, 3DES, CAST5, BLOWFISH, AES, AES192, AES256, TWOFISH,
        CAMELLIA128, CAMELLIA192, CAMELLIA256
Hash: SHA1, RIPEMD160, SHA256, SHA384, SHA512, SHA224
Compression: Uncompressed, ZIP, ZLIB, BZIP2