How can I get rid of beeps at end of voicemail?

This is kind of an odd question, but I use voicemails as a way for callers to leave stories and memories. I instruct them to press “1” after leaving their message, which is fine, but then at the end of the message you can hear the tone. If I don’t instruct them to press the “1” after leaving a message then you hear the hangup.

I know in freepbx there is a way of calling Sox after call monitoring, but it doesn’t look like there is a way to call sox after a voicemail - actually I take that back, I think I can have a special dial-plan instuction that calls a shell command, but I’m not sure what I would put in order for it to grab the right sound file, filter out the frequency of the 1 touch tone, and save the file. Any thoughts?