Atomic Mail Sender really doesn't though. It only lets you do it manually--which is USELESS.
However, with some workarounds, I was able to use the Random Word function to automate it on every mail sent. Requires a bit of work, but worth it IMO.
1. Get your spintax ready for the entire message.
2. Use and and replace on regex in a text editor like sublime text or notepad++ to turn {word1|word2|word3}, {phrase 1|phrase 2} into:
#delimiter#
word1
word2
word3
#delimiter#
,
#delimiter#
phrase 1
phrase 2
phrase 3
3. Run a script to split this file into separate files, one for each of AMS' random word variables. I used csplit with #delimiter# as my regex to trigger where the file reads up to before splitting the read-thru lines into their own files: xx00, xx01, xx02, etc.
4. Move these files to the Random Number folder in the Roaming Data folder for AMS (windows)
5. Use a short script (i just wrote a quick js loop in chrome console and console.log'ed resultant string) to concatenate all the random number variable references and paste into the AMS editor (ex. [...]%_RND_xx55%%_RND_xx56%%_RND_xx57%[...])