kristianf@ares ~ $ export MYF=$(mktemp -d)
kristianf@ares ~ $ cd $MYF
kristianf@ares /tmp/tmp.zcfri996PH $ echo "VERY VERY SECRET DATA" > secret.txt
kristianf@ares /tmp/tmp.zcfri996PH $ gpg -aer kf@sumptuouscapital.com secret.txt 
gpg: kf@sumptuouscapital.com: skipped: public key already present
kristianf@ares /tmp/tmp.zcfri996PH $ ls
secret.txt  secret.txt.asc
kristianf@ares /tmp/tmp.zcfri996PH $ gpg --show-session-key secret.txt.asc
gpg: WARNING: no command supplied.  Trying to guess what you mean ...
gpg: encrypted with 2048-bit RSA key, ID AF34B0A8161D03BE, created 2015-05-27
      "Kristian Fiskerstrand <kristian.fiskerstrand@sumptuouscapital.com>"
gpg: session key: '9:CB9BF4BD84A88FA06F015C4309FAF7177BC21D5D9C1E2B85099C33067B3A37C9'
File 'secret.txt' exists. Overwrite? (y/N) y
kristianf@ares /tmp/tmp.zcfri996PH $ gpg --override-session-key "9:CB9BF4BD84A88FA06F015C4309FAF7177BC21D5D9C1E2B85099C33067B3A37C9" --decrypt secret.txt.asc 
gpg: encrypted with 2048-bit RSA key, ID AF34B0A8161D03BE, created 2015-05-27
      "Kristian Fiskerstrand <kristian.fiskerstrand@sumptuouscapital.com>"
VERY VERY SECRET DATA